P. 436 of Theorem List - Metamath Proof Explorer

Theorem List for Metamath Proof Explorer - 43501-43600   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	wallispi 43501*	Wallis' formula for π : Wallis' product converges to π / 2 . (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐹 = (𝑘 ∈ ℕ ↦ (((2 · 𝑘) / ((2 · 𝑘) − 1)) · ((2 · 𝑘) / ((2 · 𝑘) + 1))))    &   ⊢ 𝑊 = (𝑛 ∈ ℕ ↦ (seq1( · , 𝐹)‘𝑛))    ⇒   ⊢ 𝑊 ⇝ (π / 2)
Theorem	wallispi2lem1 43502	An intermediate step between the first version of the Wallis' formula for π and the second version of Wallis' formula. This second version will then be used to prove Stirling's approximation formula for the factorial. (Contributed by Glauco Siliprandi, 30-Jun-2017.)
⊢ (𝑁 ∈ ℕ → (seq1( · , (𝑘 ∈ ℕ ↦ (((2 · 𝑘) / ((2 · 𝑘) − 1)) · ((2 · 𝑘) / ((2 · 𝑘) + 1)))))‘𝑁) = ((1 / ((2 · 𝑁) + 1)) · (seq1( · , (𝑘 ∈ ℕ ↦ (((2 · 𝑘)↑4) / (((2 · 𝑘) · ((2 · 𝑘) − 1))↑2))))‘𝑁)))
Theorem	wallispi2lem2 43503	Two expressions are proven to be equal, and this is used to complete the proof of the second version of Wallis' formula for π . (Contributed by Glauco Siliprandi, 30-Jun-2017.)
⊢ (𝑁 ∈ ℕ → (seq1( · , (𝑘 ∈ ℕ ↦ (((2 · 𝑘)↑4) / (((2 · 𝑘) · ((2 · 𝑘) − 1))↑2))))‘𝑁) = (((2↑(4 · 𝑁)) · ((!‘𝑁)↑4)) / ((!‘(2 · 𝑁))↑2)))
Theorem	wallispi2 43504	An alternative version of Wallis' formula for π ; this second formula uses factorials and it is later used to prove Stirling's approximation formula. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝑉 = (𝑛 ∈ ℕ ↦ ((((2↑(4 · 𝑛)) · ((!‘𝑛)↑4)) / ((!‘(2 · 𝑛))↑2)) / ((2 · 𝑛) + 1)))    ⇒   ⊢ 𝑉 ⇝ (π / 2)
20.37.14  Stirling's approximation formula for ` n ` factorial
Theorem	stirlinglem1 43505	A simple limit of fractions is computed. (Contributed by Glauco Siliprandi, 30-Jun-2017.)
⊢ 𝐻 = (𝑛 ∈ ℕ ↦ ((𝑛↑2) / (𝑛 · ((2 · 𝑛) + 1))))    &   ⊢ 𝐹 = (𝑛 ∈ ℕ ↦ (1 − (1 / ((2 · 𝑛) + 1))))    &   ⊢ 𝐺 = (𝑛 ∈ ℕ ↦ (1 / ((2 · 𝑛) + 1)))    &   ⊢ 𝐿 = (𝑛 ∈ ℕ ↦ (1 / 𝑛))    ⇒   ⊢ 𝐻 ⇝ (1 / 2)
Theorem	stirlinglem2 43506	𝐴 maps to positive reals. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    ⇒   ⊢ (𝑁 ∈ ℕ → (𝐴‘𝑁) ∈ ℝ+)
Theorem	stirlinglem3 43507	Long but simple algebraic transformations are applied to show that 𝑉, the Wallis formula for π , can be expressed in terms of 𝐴, the Stirling's approximation formula for the factorial, up to a constant factor. This will allow (in a later theorem) to determine the right constant factor to be put into the 𝐴, in order to get the exact Stirling's formula. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝐴‘(2 · 𝑛)))    &   ⊢ 𝐸 = (𝑛 ∈ ℕ ↦ ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛)))    &   ⊢ 𝑉 = (𝑛 ∈ ℕ ↦ ((((2↑(4 · 𝑛)) · ((!‘𝑛)↑4)) / ((!‘(2 · 𝑛))↑2)) / ((2 · 𝑛) + 1)))    ⇒   ⊢ 𝑉 = (𝑛 ∈ ℕ ↦ ((((𝐴‘𝑛)↑4) / ((𝐷‘𝑛)↑2)) · ((𝑛↑2) / (𝑛 · ((2 · 𝑛) + 1)))))
Theorem	stirlinglem4 43508*	Algebraic manipulation of ((𝐵 n ) - ( B (𝑛 + 1))). It will be used in other theorems to show that 𝐵 is decreasing. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (log‘(𝐴‘𝑛)))    &   ⊢ 𝐽 = (𝑛 ∈ ℕ ↦ ((((1 + (2 · 𝑛)) / 2) · (log‘((𝑛 + 1) / 𝑛))) − 1))    ⇒   ⊢ (𝑁 ∈ ℕ → ((𝐵‘𝑁) − (𝐵‘(𝑁 + 1))) = (𝐽‘𝑁))
Theorem	stirlinglem5 43509*	If 𝑇 is between 0 and 1, then a series (without alternating negative and positive terms) is given that converges to log((1+T)/(1-T)). (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐷 = (𝑗 ∈ ℕ ↦ ((-1↑(𝑗 − 1)) · ((𝑇↑𝑗) / 𝑗)))    &   ⊢ 𝐸 = (𝑗 ∈ ℕ ↦ ((𝑇↑𝑗) / 𝑗))    &   ⊢ 𝐹 = (𝑗 ∈ ℕ ↦ (((-1↑(𝑗 − 1)) · ((𝑇↑𝑗) / 𝑗)) + ((𝑇↑𝑗) / 𝑗)))    &   ⊢ 𝐻 = (𝑗 ∈ ℕ0 ↦ (2 · ((1 / ((2 · 𝑗) + 1)) · (𝑇↑((2 · 𝑗) + 1)))))    &   ⊢ 𝐺 = (𝑗 ∈ ℕ0 ↦ ((2 · 𝑗) + 1))    &   ⊢ (𝜑 → 𝑇 ∈ ℝ+)    &   ⊢ (𝜑 → (abs‘𝑇) < 1)    ⇒   ⊢ (𝜑 → seq0( + , 𝐻) ⇝ (log‘((1 + 𝑇) / (1 − 𝑇))))
Theorem	stirlinglem6 43510*	A series that converges to log((𝑁 + 1) / 𝑁). (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐻 = (𝑗 ∈ ℕ0 ↦ (2 · ((1 / ((2 · 𝑗) + 1)) · ((1 / ((2 · 𝑁) + 1))↑((2 · 𝑗) + 1)))))    ⇒   ⊢ (𝑁 ∈ ℕ → seq0( + , 𝐻) ⇝ (log‘((𝑁 + 1) / 𝑁)))
Theorem	stirlinglem7 43511*	Algebraic manipulation of the formula for J(n). (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐽 = (𝑛 ∈ ℕ ↦ ((((1 + (2 · 𝑛)) / 2) · (log‘((𝑛 + 1) / 𝑛))) − 1))    &   ⊢ 𝐾 = (𝑘 ∈ ℕ ↦ ((1 / ((2 · 𝑘) + 1)) · ((1 / ((2 · 𝑁) + 1))↑(2 · 𝑘))))    &   ⊢ 𝐻 = (𝑘 ∈ ℕ0 ↦ (2 · ((1 / ((2 · 𝑘) + 1)) · ((1 / ((2 · 𝑁) + 1))↑((2 · 𝑘) + 1)))))    ⇒   ⊢ (𝑁 ∈ ℕ → seq1( + , 𝐾) ⇝ (𝐽‘𝑁))
Theorem	stirlinglem8 43512	If 𝐴 converges to 𝐶, then 𝐹 converges to C^2 . (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ Ⅎ𝑛𝜑    &   ⊢ Ⅎ𝑛𝐴    &   ⊢ Ⅎ𝑛𝐷    &   ⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝐴‘(2 · 𝑛)))    &   ⊢ (𝜑 → 𝐴:ℕ⟶ℝ+)    &   ⊢ 𝐹 = (𝑛 ∈ ℕ ↦ (((𝐴‘𝑛)↑4) / ((𝐷‘𝑛)↑2)))    &   ⊢ 𝐿 = (𝑛 ∈ ℕ ↦ ((𝐴‘𝑛)↑4))    &   ⊢ 𝑀 = (𝑛 ∈ ℕ ↦ ((𝐷‘𝑛)↑2))    &   ⊢ ((𝜑 ∧ 𝑛 ∈ ℕ) → (𝐷‘𝑛) ∈ ℝ+)    &   ⊢ (𝜑 → 𝐶 ∈ ℝ+)    &   ⊢ (𝜑 → 𝐴 ⇝ 𝐶)    ⇒   ⊢ (𝜑 → 𝐹 ⇝ (𝐶↑2))
Theorem	stirlinglem9 43513*	((𝐵‘𝑁) − (𝐵‘(𝑁 + 1))) is expressed as a limit of a series. This result will be used both to prove that 𝐵 is decreasing and to prove that 𝐵 is bounded (below). It will follow that 𝐵 converges in the reals. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (log‘(𝐴‘𝑛)))    &   ⊢ 𝐽 = (𝑛 ∈ ℕ ↦ ((((1 + (2 · 𝑛)) / 2) · (log‘((𝑛 + 1) / 𝑛))) − 1))    &   ⊢ 𝐾 = (𝑘 ∈ ℕ ↦ ((1 / ((2 · 𝑘) + 1)) · ((1 / ((2 · 𝑁) + 1))↑(2 · 𝑘))))    ⇒   ⊢ (𝑁 ∈ ℕ → seq1( + , 𝐾) ⇝ ((𝐵‘𝑁) − (𝐵‘(𝑁 + 1))))
Theorem	stirlinglem10 43514*	A bound for any B(N)-B(N + 1) that will allow to find a lower bound for the whole 𝐵 sequence. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (log‘(𝐴‘𝑛)))    &   ⊢ 𝐾 = (𝑘 ∈ ℕ ↦ ((1 / ((2 · 𝑘) + 1)) · ((1 / ((2 · 𝑁) + 1))↑(2 · 𝑘))))    &   ⊢ 𝐿 = (𝑘 ∈ ℕ ↦ ((1 / (((2 · 𝑁) + 1)↑2))↑𝑘))    ⇒   ⊢ (𝑁 ∈ ℕ → ((𝐵‘𝑁) − (𝐵‘(𝑁 + 1))) ≤ ((1 / 4) · (1 / (𝑁 · (𝑁 + 1)))))
Theorem	stirlinglem11 43515*	𝐵 is decreasing. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (log‘(𝐴‘𝑛)))    &   ⊢ 𝐾 = (𝑘 ∈ ℕ ↦ ((1 / ((2 · 𝑘) + 1)) · ((1 / ((2 · 𝑁) + 1))↑(2 · 𝑘))))    ⇒   ⊢ (𝑁 ∈ ℕ → (𝐵‘(𝑁 + 1)) < (𝐵‘𝑁))
Theorem	stirlinglem12 43516*	The sequence 𝐵 is bounded below. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (log‘(𝐴‘𝑛)))    &   ⊢ 𝐹 = (𝑛 ∈ ℕ ↦ (1 / (𝑛 · (𝑛 + 1))))    ⇒   ⊢ (𝑁 ∈ ℕ → ((𝐵‘1) − (1 / 4)) ≤ (𝐵‘𝑁))
Theorem	stirlinglem13 43517*	𝐵 is decreasing and has a lower bound, then it converges. Since 𝐵 is log𝐴, in another theorem it is proven that 𝐴 converges as well. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (log‘(𝐴‘𝑛)))    ⇒   ⊢ ∃𝑑 ∈ ℝ 𝐵 ⇝ 𝑑
Theorem	stirlinglem14 43518*	The sequence 𝐴 converges to a positive real. This proves that the Stirling's formula converges to the factorial, up to a constant. In another theorem, using Wallis' formula for π& , such constant is exactly determined, thus proving the Stirling's formula. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (log‘(𝐴‘𝑛)))    ⇒   ⊢ ∃𝑐 ∈ ℝ+ 𝐴 ⇝ 𝑐
Theorem	stirlinglem15 43519*	The Stirling's formula is proven using a number of local definitions. The main theorem stirling 43520 will use this final lemma, but it will not expose the local definitions. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ Ⅎ𝑛𝜑    &   ⊢ 𝑆 = (𝑛 ∈ ℕ0 ↦ ((√‘((2 · π) · 𝑛)) · ((𝑛 / e)↑𝑛)))    &   ⊢ 𝐴 = (𝑛 ∈ ℕ ↦ ((!‘𝑛) / ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛))))    &   ⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝐴‘(2 · 𝑛)))    &   ⊢ 𝐸 = (𝑛 ∈ ℕ ↦ ((√‘(2 · 𝑛)) · ((𝑛 / e)↑𝑛)))    &   ⊢ 𝑉 = (𝑛 ∈ ℕ ↦ ((((2↑(4 · 𝑛)) · ((!‘𝑛)↑4)) / ((!‘(2 · 𝑛))↑2)) / ((2 · 𝑛) + 1)))    &   ⊢ 𝐹 = (𝑛 ∈ ℕ ↦ (((𝐴‘𝑛)↑4) / ((𝐷‘𝑛)↑2)))    &   ⊢ 𝐻 = (𝑛 ∈ ℕ ↦ ((𝑛↑2) / (𝑛 · ((2 · 𝑛) + 1))))    &   ⊢ (𝜑 → 𝐶 ∈ ℝ+)    &   ⊢ (𝜑 → 𝐴 ⇝ 𝐶)    ⇒   ⊢ (𝜑 → (𝑛 ∈ ℕ ↦ ((!‘𝑛) / (𝑆‘𝑛))) ⇝ 1)
Theorem	stirling 43520	Stirling's approximation formula for 𝑛 factorial. The proof follows two major steps: first it is proven that 𝑆 and 𝑛 factorial are asymptotically equivalent, up to an unknown constant. Then, using Wallis' formula for π it is proven that the unknown constant is the square root of π and then the exact Stirling's formula is established. This is Metamath 100 proof #90. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝑆 = (𝑛 ∈ ℕ0 ↦ ((√‘((2 · π) · 𝑛)) · ((𝑛 / e)↑𝑛)))    ⇒   ⊢ (𝑛 ∈ ℕ ↦ ((!‘𝑛) / (𝑆‘𝑛))) ⇝ 1
Theorem	stirlingr 43521	Stirling's approximation formula for 𝑛 factorial: here convergence is expressed with respect to the standard topology on the reals. The main theorem stirling 43520 is proven for convergence in the topology of complex numbers. The variable 𝑅 is used to denote convergence with respect to the standard topology on the reals. (Contributed by Glauco Siliprandi, 29-Jun-2017.)
⊢ 𝑆 = (𝑛 ∈ ℕ0 ↦ ((√‘((2 · π) · 𝑛)) · ((𝑛 / e)↑𝑛)))    &   ⊢ 𝑅 = (⇝𝑡‘(topGen‘ran (,)))    ⇒   ⊢ (𝑛 ∈ ℕ ↦ ((!‘𝑛) / (𝑆‘𝑛)))𝑅1
20.37.15  Dirichlet kernel
Theorem	dirkerval 43522*	The Nth Dirichlet Kernel. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑠 ∈ ℝ ↦ if((𝑠 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑠)) / ((2 · π) · (sin‘(𝑠 / 2)))))))    ⇒   ⊢ (𝑁 ∈ ℕ → (𝐷‘𝑁) = (𝑠 ∈ ℝ ↦ if((𝑠 mod (2 · π)) = 0, (((2 · 𝑁) + 1) / (2 · π)), ((sin‘((𝑁 + (1 / 2)) · 𝑠)) / ((2 · π) · (sin‘(𝑠 / 2)))))))
Theorem	dirker2re 43523	The Dirichlet Kernel value is a real if the argument is not a multiple of π . (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (((𝑁 ∈ ℕ ∧ 𝑆 ∈ ℝ) ∧ ¬ (𝑆 mod (2 · π)) = 0) → ((sin‘((𝑁 + (1 / 2)) · 𝑆)) / ((2 · π) · (sin‘(𝑆 / 2)))) ∈ ℝ)
Theorem	dirkerdenne0 43524	The Dirichlet Kernel denominator is never 0. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ ((𝑆 ∈ ℝ ∧ ¬ (𝑆 mod (2 · π)) = 0) → ((2 · π) · (sin‘(𝑆 / 2))) ≠ 0)
Theorem	dirkerval2 43525*	The Nth Dirichlet Kernel evaluated at a specific point 𝑆. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑠 ∈ ℝ ↦ if((𝑠 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑠)) / ((2 · π) · (sin‘(𝑠 / 2)))))))    ⇒   ⊢ ((𝑁 ∈ ℕ ∧ 𝑆 ∈ ℝ) → ((𝐷‘𝑁)‘𝑆) = if((𝑆 mod (2 · π)) = 0, (((2 · 𝑁) + 1) / (2 · π)), ((sin‘((𝑁 + (1 / 2)) · 𝑆)) / ((2 · π) · (sin‘(𝑆 / 2))))))
Theorem	dirkerre 43526*	The Dirichlet Kernel at any point evaluates to a real. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑠 ∈ ℝ ↦ if((𝑠 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑠)) / ((2 · π) · (sin‘(𝑠 / 2)))))))    ⇒   ⊢ ((𝑁 ∈ ℕ ∧ 𝑆 ∈ ℝ) → ((𝐷‘𝑁)‘𝑆) ∈ ℝ)
Theorem	dirkerper 43527*	the Dirichlet Kernel has period 2π. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑦 ∈ ℝ ↦ if((𝑦 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑦)) / ((2 · π) · (sin‘(𝑦 / 2)))))))    &   ⊢ 𝑇 = (2 · π)    ⇒   ⊢ ((𝑁 ∈ ℕ ∧ 𝑥 ∈ ℝ) → ((𝐷‘𝑁)‘(𝑥 + 𝑇)) = ((𝐷‘𝑁)‘𝑥))
Theorem	dirkerf 43528*	For any natural number 𝑁, the Dirichlet Kernel (𝐷‘𝑁) is a function. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑦 ∈ ℝ ↦ if((𝑦 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑦)) / ((2 · π) · (sin‘(𝑦 / 2)))))))    ⇒   ⊢ (𝑁 ∈ ℕ → (𝐷‘𝑁):ℝ⟶ℝ)
Theorem	dirkertrigeqlem1 43529*	Sum of an even number of alternating cos values. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝐾 ∈ ℕ → Σ𝑛 ∈ (1...(2 · 𝐾))(cos‘(𝑛 · π)) = 0)
Theorem	dirkertrigeqlem2 43530*	Trigonomic equality lemma for the Dirichlet Kernel trigonomic equality. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → (sin‘𝐴) ≠ 0)    &   ⊢ (𝜑 → 𝑁 ∈ ℕ)    ⇒   ⊢ (𝜑 → (((1 / 2) + Σ𝑛 ∈ (1...𝑁)(cos‘(𝑛 · 𝐴))) / π) = ((sin‘((𝑁 + (1 / 2)) · 𝐴)) / ((2 · π) · (sin‘(𝐴 / 2)))))
Theorem	dirkertrigeqlem3 43531*	Trigonometric equality lemma for the Dirichlet Kernel trigonometric equality. Here we handle the case for an angle that's an odd multiple of π. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝑁 ∈ ℕ)    &   ⊢ (𝜑 → 𝐾 ∈ ℤ)    &   ⊢ 𝐴 = (((2 · 𝐾) + 1) · π)    ⇒   ⊢ (𝜑 → (((1 / 2) + Σ𝑛 ∈ (1...𝑁)(cos‘(𝑛 · 𝐴))) / π) = ((sin‘((𝑁 + (1 / 2)) · 𝐴)) / ((2 · π) · (sin‘(𝐴 / 2)))))
Theorem	dirkertrigeq 43532*	Trigonometric equality for the Dirichlet kernel. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑠 ∈ ℝ ↦ if((𝑠 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑠)) / ((2 · π) · (sin‘(𝑠 / 2)))))))    &   ⊢ (𝜑 → 𝑁 ∈ ℕ)    &   ⊢ 𝐹 = (𝐷‘𝑁)    &   ⊢ 𝐻 = (𝑠 ∈ ℝ ↦ (((1 / 2) + Σ𝑘 ∈ (1...𝑁)(cos‘(𝑘 · 𝑠))) / π))    ⇒   ⊢ (𝜑 → 𝐹 = 𝐻)
Theorem	dirkeritg 43533*	The definite integral of the Dirichlet Kernel. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑥 ∈ ℝ ↦ if((𝑥 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑥)) / ((2 · π) · (sin‘(𝑥 / 2)))))))    &   ⊢ (𝜑 → 𝑁 ∈ ℕ)    &   ⊢ 𝐹 = (𝐷‘𝑁)    &   ⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 ≤ 𝐵)    &   ⊢ 𝐺 = (𝑥 ∈ (𝐴[,]𝐵) ↦ (((𝑥 / 2) + Σ𝑘 ∈ (1...𝑁)((sin‘(𝑘 · 𝑥)) / 𝑘)) / π))    ⇒   ⊢ (𝜑 → ∫(𝐴(,)𝐵)(𝐹‘𝑥) d𝑥 = ((𝐺‘𝐵) − (𝐺‘𝐴)))
Theorem	dirkercncflem1 43534*	If 𝑌 is a multiple of π then it belongs to an open inerval (𝐴(,)𝐵) such that for any other point 𝑦 in the interval, cos y/2 and sin y/2 are nonzero. Such an interval is needed to apply De L'Hopital theorem. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐴 = (𝑌 − π)    &   ⊢ 𝐵 = (𝑌 + π)    &   ⊢ (𝜑 → 𝑌 ∈ ℝ)    &   ⊢ (𝜑 → (𝑌 mod (2 · π)) = 0)    ⇒   ⊢ (𝜑 → (𝑌 ∈ (𝐴(,)𝐵) ∧ ∀𝑦 ∈ ((𝐴(,)𝐵) ∖ {𝑌})((sin‘(𝑦 / 2)) ≠ 0 ∧ (cos‘(𝑦 / 2)) ≠ 0)))
Theorem	dirkercncflem2 43535*	Lemma used to prove that the Dirichlet Kernel is continuous at 𝑌 points that are multiples of (2 · π). (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑦 ∈ ℝ ↦ if((𝑦 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑦)) / ((2 · π) · (sin‘(𝑦 / 2)))))))    &   ⊢ 𝐹 = (𝑦 ∈ ((𝐴(,)𝐵) ∖ {𝑌}) ↦ (sin‘((𝑁 + (1 / 2)) · 𝑦)))    &   ⊢ 𝐺 = (𝑦 ∈ ((𝐴(,)𝐵) ∖ {𝑌}) ↦ ((2 · π) · (sin‘(𝑦 / 2))))    &   ⊢ ((𝜑 ∧ 𝑦 ∈ ((𝐴(,)𝐵) ∖ {𝑌})) → (sin‘(𝑦 / 2)) ≠ 0)    &   ⊢ 𝐻 = (𝑦 ∈ ((𝐴(,)𝐵) ∖ {𝑌}) ↦ ((𝑁 + (1 / 2)) · (cos‘((𝑁 + (1 / 2)) · 𝑦))))    &   ⊢ 𝐼 = (𝑦 ∈ ((𝐴(,)𝐵) ∖ {𝑌}) ↦ (π · (cos‘(𝑦 / 2))))    &   ⊢ 𝐿 = (𝑤 ∈ (𝐴(,)𝐵) ↦ (((𝑁 + (1 / 2)) · (cos‘((𝑁 + (1 / 2)) · 𝑤))) / (π · (cos‘(𝑤 / 2)))))    &   ⊢ (𝜑 → 𝑁 ∈ ℕ)    &   ⊢ (𝜑 → 𝑌 ∈ (𝐴(,)𝐵))    &   ⊢ (𝜑 → (𝑌 mod (2 · π)) = 0)    &   ⊢ ((𝜑 ∧ 𝑦 ∈ ((𝐴(,)𝐵) ∖ {𝑌})) → (cos‘(𝑦 / 2)) ≠ 0)    ⇒   ⊢ (𝜑 → ((𝐷‘𝑁)‘𝑌) ∈ (((𝐷‘𝑁) ↾ ((𝐴(,)𝐵) ∖ {𝑌})) limℂ 𝑌))
Theorem	dirkercncflem3 43536*	The Dirichlet Kernel is continuous at 𝑌 points that are multiples of (2 · π). (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑦 ∈ ℝ ↦ if((𝑦 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑦)) / ((2 · π) · (sin‘(𝑦 / 2)))))))    &   ⊢ 𝐴 = (𝑌 − π)    &   ⊢ 𝐵 = (𝑌 + π)    &   ⊢ 𝐹 = (𝑦 ∈ (𝐴(,)𝐵) ↦ ((sin‘((𝑛 + (1 / 2)) · 𝑦)) / ((2 · π) · (sin‘(𝑦 / 2)))))    &   ⊢ 𝐺 = (𝑦 ∈ (𝐴(,)𝐵) ↦ ((2 · π) · (sin‘(𝑦 / 2))))    &   ⊢ (𝜑 → 𝑁 ∈ ℕ)    &   ⊢ (𝜑 → 𝑌 ∈ ℝ)    &   ⊢ (𝜑 → (𝑌 mod (2 · π)) = 0)    ⇒   ⊢ (𝜑 → ((𝐷‘𝑁)‘𝑌) ∈ ((𝐷‘𝑁) limℂ 𝑌))
Theorem	dirkercncflem4 43537*	The Dirichlet Kernel is continuos at points that are not multiple of 2 π . This is the easier condition, for the proof of the continuity of the Dirichlet kernel. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑦 ∈ ℝ ↦ if((𝑦 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑦)) / ((2 · π) · (sin‘(𝑦 / 2)))))))    &   ⊢ (𝜑 → 𝑁 ∈ ℕ)    &   ⊢ (𝜑 → 𝑌 ∈ ℝ)    &   ⊢ (𝜑 → (𝑌 mod (2 · π)) ≠ 0)    &   ⊢ 𝐴 = (⌊‘(𝑌 / (2 · π)))    &   ⊢ 𝐵 = (𝐴 + 1)    &   ⊢ 𝐶 = (𝐴 · (2 · π))    &   ⊢ 𝐸 = (𝐵 · (2 · π))    ⇒   ⊢ (𝜑 → (𝐷‘𝑁) ∈ (((topGen‘ran (,)) CnP (topGen‘ran (,)))‘𝑌))
Theorem	dirkercncf 43538*	For any natural number 𝑁, the Dirichlet Kernel (𝐷‘𝑁) is continuous. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐷 = (𝑛 ∈ ℕ ↦ (𝑦 ∈ ℝ ↦ if((𝑦 mod (2 · π)) = 0, (((2 · 𝑛) + 1) / (2 · π)), ((sin‘((𝑛 + (1 / 2)) · 𝑦)) / ((2 · π) · (sin‘(𝑦 / 2)))))))    ⇒   ⊢ (𝑁 ∈ ℕ → (𝐷‘𝑁) ∈ (ℝ–cn→ℝ))
20.37.16  Fourier Series
Theorem	fourierdlem1 43539	A partition interval is a subset of the partitioned interval. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ*)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ*)    &   ⊢ (𝜑 → 𝑄:(0...𝑀)⟶(𝐴[,]𝐵))    &   ⊢ (𝜑 → 𝐼 ∈ (0..^𝑀))    &   ⊢ (𝜑 → 𝑋 ∈ ((𝑄‘𝐼)[,](𝑄‘(𝐼 + 1))))    ⇒   ⊢ (𝜑 → 𝑋 ∈ (𝐴[,]𝐵))
Theorem	fourierdlem2 43540*	Membership in a partition. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    ⇒   ⊢ (𝑀 ∈ ℕ → (𝑄 ∈ (𝑃‘𝑀) ↔ (𝑄 ∈ (ℝ ↑m (0...𝑀)) ∧ (((𝑄‘0) = 𝐴 ∧ (𝑄‘𝑀) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑀)(𝑄‘𝑖) < (𝑄‘(𝑖 + 1))))))
Theorem	fourierdlem3 43541*	Membership in a partition. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ ((-π[,]π) ↑m (0...𝑚)) ∣ (((𝑝‘0) = -π ∧ (𝑝‘𝑚) = π) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    ⇒   ⊢ (𝑀 ∈ ℕ → (𝑄 ∈ (𝑃‘𝑀) ↔ (𝑄 ∈ ((-π[,]π) ↑m (0...𝑀)) ∧ (((𝑄‘0) = -π ∧ (𝑄‘𝑀) = π) ∧ ∀𝑖 ∈ (0..^𝑀)(𝑄‘𝑖) < (𝑄‘(𝑖 + 1))))))
Theorem	fourierdlem4 43542*	𝐸 is a function that maps any point to a periodic corresponding point in (𝐴, 𝐵]. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇)))    ⇒   ⊢ (𝜑 → 𝐸:ℝ⟶(𝐴(,]𝐵))
Theorem	fourierdlem5 43543*	𝑆 is a function. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑆 = (𝑥 ∈ (-π[,]π) ↦ (sin‘((𝑋 + (1 / 2)) · 𝑥)))    ⇒   ⊢ (𝑋 ∈ ℝ → 𝑆:(-π[,]π)⟶ℝ)
Theorem	fourierdlem6 43544	𝑋 is in the periodic partition, when the considered interval is centered at 𝑋. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝐼 ∈ ℤ)    &   ⊢ (𝜑 → 𝐽 ∈ ℤ)    &   ⊢ (𝜑 → 𝐼 < 𝐽)    &   ⊢ (𝜑 → (𝑋 + (𝐼 · 𝑇)) ∈ (𝐴[,]𝐵))    &   ⊢ (𝜑 → (𝑋 + (𝐽 · 𝑇)) ∈ (𝐴[,]𝐵))    ⇒   ⊢ (𝜑 → 𝐽 = (𝐼 + 1))
Theorem	fourierdlem7 43545*	The difference between the periodic sawtooth function and the identity function is decreasing. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇)))    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝑌 ∈ ℝ)    &   ⊢ (𝜑 → 𝑋 ≤ 𝑌)    ⇒   ⊢ (𝜑 → ((𝐸‘𝑌) − 𝑌) ≤ ((𝐸‘𝑋) − 𝑋))
Theorem	fourierdlem8 43546	A partition interval is a subset of the partitioned interval. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ*)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ*)    &   ⊢ (𝜑 → 𝑄:(0...𝑀)⟶(𝐴[,]𝐵))    &   ⊢ (𝜑 → 𝐼 ∈ (0..^𝑀))    ⇒   ⊢ (𝜑 → ((𝑄‘𝐼)[,](𝑄‘(𝐼 + 1))) ⊆ (𝐴[,]𝐵))
Theorem	fourierdlem9 43547*	𝐻 is a complex function. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝑌 ∈ ℝ)    &   ⊢ (𝜑 → 𝑊 ∈ ℝ)    &   ⊢ 𝐻 = (𝑠 ∈ (-π[,]π) ↦ if(𝑠 = 0, 0, (((𝐹‘(𝑋 + 𝑠)) − if(0 < 𝑠, 𝑌, 𝑊)) / 𝑠)))    ⇒   ⊢ (𝜑 → 𝐻:(-π[,]π)⟶ℝ)
Theorem	fourierdlem10 43548	Condition on the bounds of a nonempty subinterval. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ (𝜑 → 𝐷 ∈ ℝ)    &   ⊢ (𝜑 → 𝐶 < 𝐷)    &   ⊢ (𝜑 → (𝐶(,)𝐷) ⊆ (𝐴(,)𝐵))    ⇒   ⊢ (𝜑 → (𝐴 ≤ 𝐶 ∧ 𝐷 ≤ 𝐵))
Theorem	fourierdlem11 43549*	If there is a partition, than the lower bound is strictly less than the upper bound. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    ⇒   ⊢ (𝜑 → (𝐴 ∈ ℝ ∧ 𝐵 ∈ ℝ ∧ 𝐴 < 𝐵))
Theorem	fourierdlem12 43550*	A point of a partition is not an element of any open interval determined by the partition. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    &   ⊢ (𝜑 → 𝑋 ∈ ran 𝑄)    ⇒   ⊢ ((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) → ¬ 𝑋 ∈ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1))))
Theorem	fourierdlem13 43551*	Value of 𝑉 in terms of value of 𝑄. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = (𝐴 + 𝑋) ∧ (𝑝‘𝑚) = (𝐵 + 𝑋)) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑉 ∈ (𝑃‘𝑀))    &   ⊢ (𝜑 → 𝐼 ∈ (0...𝑀))    &   ⊢ 𝑄 = (𝑖 ∈ (0...𝑀) ↦ ((𝑉‘𝑖) − 𝑋))    ⇒   ⊢ (𝜑 → ((𝑄‘𝐼) = ((𝑉‘𝐼) − 𝑋) ∧ (𝑉‘𝐼) = (𝑋 + (𝑄‘𝐼))))
Theorem	fourierdlem14 43552*	Given the partition 𝑉, 𝑄 is the partition shifted to the left by 𝑋. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = (𝐴 + 𝑋) ∧ (𝑝‘𝑚) = (𝐵 + 𝑋)) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ 𝑂 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑉 ∈ (𝑃‘𝑀))    &   ⊢ 𝑄 = (𝑖 ∈ (0...𝑀) ↦ ((𝑉‘𝑖) − 𝑋))    ⇒   ⊢ (𝜑 → 𝑄 ∈ (𝑂‘𝑀))
Theorem	fourierdlem15 43553*	The range of the partition is between its starting point and its ending point. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    ⇒   ⊢ (𝜑 → 𝑄:(0...𝑀)⟶(𝐴[,]𝐵))
Theorem	fourierdlem16 43554*	The coefficients of the fourier series are integrable and reals. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ 𝐶 = (-π(,)π)    &   ⊢ (𝜑 → (𝐹 ↾ 𝐶) ∈ 𝐿1)    &   ⊢ 𝐴 = (𝑛 ∈ ℕ0 ↦ (∫𝐶((𝐹‘𝑥) · (cos‘(𝑛 · 𝑥))) d𝑥 / π))    &   ⊢ (𝜑 → 𝑁 ∈ ℕ0)    ⇒   ⊢ (𝜑 → (((𝐴‘𝑁) ∈ ℝ ∧ (𝑥 ∈ 𝐶 ↦ (𝐹‘𝑥)) ∈ 𝐿1) ∧ ∫𝐶((𝐹‘𝑥) · (cos‘(𝑁 · 𝑥))) d𝑥 ∈ ℝ))
Theorem	fourierdlem17 43555*	The defined 𝐿 is actually a function. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝐿 = (𝑥 ∈ (𝐴(,]𝐵) ↦ if(𝑥 = 𝐵, 𝐴, 𝑥))    ⇒   ⊢ (𝜑 → 𝐿:(𝐴(,]𝐵)⟶(𝐴[,]𝐵))
Theorem	fourierdlem18 43556*	The function 𝑆 is continuous. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝑁 ∈ ℝ)    &   ⊢ 𝑆 = (𝑠 ∈ (-π[,]π) ↦ (sin‘((𝑁 + (1 / 2)) · 𝑠)))    ⇒   ⊢ (𝜑 → 𝑆 ∈ ((-π[,]π)–cn→ℝ))
Theorem	fourierdlem19 43557*	If two elements of 𝐷 have the same periodic image in (𝐴(,]𝐵) then they are equal. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ 𝐷 = {𝑦 ∈ ((𝐴 + 𝑋)(,](𝐵 + 𝑋)) ∣ ∃𝑘 ∈ ℤ (𝑦 + (𝑘 · 𝑇)) ∈ 𝐶}    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇)))    &   ⊢ (𝜑 → 𝑊 ∈ 𝐷)    &   ⊢ (𝜑 → 𝑍 ∈ 𝐷)    &   ⊢ (𝜑 → (𝐸‘𝑍) = (𝐸‘𝑊))    ⇒   ⊢ (𝜑 → ¬ 𝑊 < 𝑍)
Theorem	fourierdlem20 43558*	Every interval in the partition 𝑆 is included in an interval of the partition 𝑄. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 ≤ 𝐵)    &   ⊢ (𝜑 → 𝑄:(0...𝑀)⟶ℝ)    &   ⊢ (𝜑 → (𝑄‘0) ≤ 𝐴)    &   ⊢ (𝜑 → 𝐵 ≤ (𝑄‘𝑀))    &   ⊢ (𝜑 → 𝐽 ∈ (0..^𝑁))    &   ⊢ 𝑇 = ({𝐴, 𝐵} ∪ (ran 𝑄 ∩ (𝐴(,)𝐵)))    &   ⊢ (𝜑 → 𝑆 Isom < , < ((0...𝑁), 𝑇))    &   ⊢ 𝐼 = sup({𝑘 ∈ (0..^𝑀) ∣ (𝑄‘𝑘) ≤ (𝑆‘𝐽)}, ℝ, < )    ⇒   ⊢ (𝜑 → ∃𝑖 ∈ (0..^𝑀)((𝑆‘𝐽)(,)(𝑆‘(𝐽 + 1))) ⊆ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1))))
Theorem	fourierdlem21 43559*	The coefficients of the fourier series are integrable and reals. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ 𝐶 = (-π(,)π)    &   ⊢ (𝜑 → (𝐹 ↾ 𝐶) ∈ 𝐿1)    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (∫𝐶((𝐹‘𝑥) · (sin‘(𝑛 · 𝑥))) d𝑥 / π))    &   ⊢ (𝜑 → 𝑁 ∈ ℕ)    ⇒   ⊢ (𝜑 → (((𝐵‘𝑁) ∈ ℝ ∧ (𝑥 ∈ 𝐶 ↦ ((𝐹‘𝑥) · (sin‘(𝑁 · 𝑥)))) ∈ 𝐿1) ∧ ∫𝐶((𝐹‘𝑥) · (sin‘(𝑁 · 𝑥))) d𝑥 ∈ ℝ))
Theorem	fourierdlem22 43560*	The coefficients of the fourier series are integrable and reals. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ 𝐶 = (-π(,)π)    &   ⊢ (𝜑 → (𝐹 ↾ 𝐶) ∈ 𝐿1)    &   ⊢ 𝐴 = (𝑛 ∈ ℕ0 ↦ (∫𝐶((𝐹‘𝑥) · (cos‘(𝑛 · 𝑥))) d𝑥 / π))    &   ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (∫𝐶((𝐹‘𝑥) · (sin‘(𝑛 · 𝑥))) d𝑥 / π))    ⇒   ⊢ (𝜑 → ((𝑛 ∈ ℕ0 → (𝐴‘𝑛) ∈ ℝ) ∧ (𝑛 ∈ ℕ → (𝐵‘𝑛) ∈ ℝ)))
Theorem	fourierdlem23 43561*	If 𝐹 is continuous and 𝑋 is constant, then (𝐹‘(𝑋 + 𝑠)) is continuous. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ⊆ ℂ)    &   ⊢ (𝜑 → 𝐹 ∈ (𝐴–cn→ℂ))    &   ⊢ (𝜑 → 𝐵 ⊆ ℂ)    &   ⊢ (𝜑 → 𝑋 ∈ ℂ)    &   ⊢ ((𝜑 ∧ 𝑠 ∈ 𝐵) → (𝑋 + 𝑠) ∈ 𝐴)    ⇒   ⊢ (𝜑 → (𝑠 ∈ 𝐵 ↦ (𝐹‘(𝑋 + 𝑠))) ∈ (𝐵–cn→ℂ))
Theorem	fourierdlem24 43562	A sufficient condition for module being nonzero. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝐴 ∈ ((-π[,]π) ∖ {0}) → (𝐴 mod (2 · π)) ≠ 0)
Theorem	fourierdlem25 43563*	If 𝐶 is not in the range of the partition, then it is in an open interval induced by the partition. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄:(0...𝑀)⟶ℝ)    &   ⊢ (𝜑 → 𝐶 ∈ ((𝑄‘0)[,](𝑄‘𝑀)))    &   ⊢ (𝜑 → ¬ 𝐶 ∈ ran 𝑄)    &   ⊢ 𝐼 = sup({𝑘 ∈ (0..^𝑀) ∣ (𝑄‘𝑘) < 𝐶}, ℝ, < )    ⇒   ⊢ (𝜑 → ∃𝑗 ∈ (0..^𝑀)𝐶 ∈ ((𝑄‘𝑗)(,)(𝑄‘(𝑗 + 1))))
Theorem	fourierdlem26 43564*	Periodic image of a point 𝑌 that's in the period that begins with the point 𝑋. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇)))    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → (𝐸‘𝑋) = 𝐵)    &   ⊢ (𝜑 → 𝑌 ∈ (𝑋(,](𝑋 + 𝑇)))    ⇒   ⊢ (𝜑 → (𝐸‘𝑌) = (𝐴 + (𝑌 − 𝑋)))
Theorem	fourierdlem27 43565	A partition open interval is a subset of the partitioned open interval. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ*)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ*)    &   ⊢ (𝜑 → 𝑄:(0...𝑀)⟶(𝐴[,]𝐵))    &   ⊢ (𝜑 → 𝐼 ∈ (0..^𝑀))    ⇒   ⊢ (𝜑 → ((𝑄‘𝐼)(,)(𝑄‘(𝐼 + 1))) ⊆ (𝐴(,)𝐵))
Theorem	fourierdlem28 43566*	Derivative of (𝐹‘(𝑋 + 𝑠)). (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ 𝐷 = (ℝ D (𝐹 ↾ ((𝑋 + 𝐴)(,)(𝑋 + 𝐵))))    &   ⊢ (𝜑 → 𝐷:((𝑋 + 𝐴)(,)(𝑋 + 𝐵))⟶ℝ)    ⇒   ⊢ (𝜑 → (ℝ D (𝑠 ∈ (𝐴(,)𝐵) ↦ (𝐹‘(𝑋 + 𝑠)))) = (𝑠 ∈ (𝐴(,)𝐵) ↦ (𝐷‘(𝑋 + 𝑠))))
Theorem	fourierdlem29 43567*	Explicit function value for 𝐾 applied to 𝐴. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐾 = (𝑠 ∈ (-π[,]π) ↦ if(𝑠 = 0, 1, (𝑠 / (2 · (sin‘(𝑠 / 2))))))    ⇒   ⊢ (𝐴 ∈ (-π[,]π) → (𝐾‘𝐴) = if(𝐴 = 0, 1, (𝐴 / (2 · (sin‘(𝐴 / 2))))))
Theorem	fourierdlem30 43568*	Sum of three small pieces is less than ε. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → (𝑥 ∈ 𝐼 ↦ (𝐹 · -𝐺)) ∈ 𝐿1)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐼) → 𝐹 ∈ ℂ)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐼) → 𝐺 ∈ ℂ)    &   ⊢ (𝜑 → 𝐴 ∈ ℂ)    &   ⊢ 𝑋 = (abs‘𝐴)    &   ⊢ (𝜑 → 𝐶 ∈ ℂ)    &   ⊢ 𝑌 = (abs‘𝐶)    &   ⊢ 𝑍 = (abs‘∫𝐼(𝐹 · -𝐺) d𝑥)    &   ⊢ (𝜑 → 𝐸 ∈ ℝ+)    &   ⊢ (𝜑 → 𝑅 ∈ ℝ)    &   ⊢ (𝜑 → ((((𝑋 + 𝑌) + 𝑍) / 𝐸) + 1) ≤ 𝑅)    &   ⊢ (𝜑 → 𝐵 ∈ ℂ)    &   ⊢ (𝜑 → (abs‘𝐵) ≤ 1)    &   ⊢ (𝜑 → 𝐷 ∈ ℂ)    &   ⊢ (𝜑 → (abs‘𝐷) ≤ 1)    ⇒   ⊢ (𝜑 → (abs‘(((𝐴 · -(𝐵 / 𝑅)) − (𝐶 · -(𝐷 / 𝑅))) − ∫𝐼(𝐹 · -(𝐺 / 𝑅)) d𝑥)) < 𝐸)
Theorem	fourierdlem31 43569*	If 𝐴 is finite and for any element in 𝐴 there is a number 𝑚 such that a property holds for all numbers larger than 𝑚, then there is a number 𝑛 such that the property holds for all numbers larger than 𝑛 and for all elements in 𝐴. (Contributed by Glauco Siliprandi, 11-Dec-2019.) (Revised by AV, 29-Sep-2020.)
⊢ Ⅎ𝑖𝜑    &   ⊢ Ⅎ𝑟𝜑    &   ⊢ Ⅎ𝑖𝑉    &   ⊢ (𝜑 → 𝐴 ∈ Fin)    &   ⊢ (𝜑 → ∀𝑖 ∈ 𝐴 ∃𝑚 ∈ ℕ ∀𝑟 ∈ (𝑚(,)+∞)𝜒)    &   ⊢ 𝑀 = {𝑚 ∈ ℕ ∣ ∀𝑟 ∈ (𝑚(,)+∞)𝜒}    &   ⊢ 𝑉 = (𝑖 ∈ 𝐴 ↦ inf(𝑀, ℝ, < ))    &   ⊢ 𝑁 = sup(ran 𝑉, ℝ, < )    ⇒   ⊢ (𝜑 → ∃𝑛 ∈ ℕ ∀𝑟 ∈ (𝑛(,)+∞)∀𝑖 ∈ 𝐴 𝜒)
Theorem	fourierdlem32 43570	Limit of a continuous function on an open subinterval. Lower bound version. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ (𝜑 → 𝐹 ∈ ((𝐴(,)𝐵)–cn→ℂ))    &   ⊢ (𝜑 → 𝑅 ∈ (𝐹 limℂ 𝐴))    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ (𝜑 → 𝐷 ∈ ℝ)    &   ⊢ (𝜑 → 𝐶 < 𝐷)    &   ⊢ (𝜑 → (𝐶(,)𝐷) ⊆ (𝐴(,)𝐵))    &   ⊢ 𝑌 = if(𝐶 = 𝐴, 𝑅, (𝐹‘𝐶))    &   ⊢ 𝐽 = ((TopOpen‘ℂfld) ↾t (𝐴[,)𝐵))    ⇒   ⊢ (𝜑 → 𝑌 ∈ ((𝐹 ↾ (𝐶(,)𝐷)) limℂ 𝐶))
Theorem	fourierdlem33 43571	Limit of a continuous function on an open subinterval. Upper bound version. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ (𝜑 → 𝐹 ∈ ((𝐴(,)𝐵)–cn→ℂ))    &   ⊢ (𝜑 → 𝐿 ∈ (𝐹 limℂ 𝐵))    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ (𝜑 → 𝐷 ∈ ℝ)    &   ⊢ (𝜑 → 𝐶 < 𝐷)    &   ⊢ (𝜑 → (𝐶(,)𝐷) ⊆ (𝐴(,)𝐵))    &   ⊢ 𝑌 = if(𝐷 = 𝐵, 𝐿, (𝐹‘𝐷))    &   ⊢ 𝐽 = ((TopOpen‘ℂfld) ↾t ((𝐴(,)𝐵) ∪ {𝐵}))    ⇒   ⊢ (𝜑 → 𝑌 ∈ ((𝐹 ↾ (𝐶(,)𝐷)) limℂ 𝐷))
Theorem	fourierdlem34 43572*	A partition is one to one. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    ⇒   ⊢ (𝜑 → 𝑄:(0...𝑀)–1-1→ℝ)
Theorem	fourierdlem35 43573	There is a single point in (𝐴(,]𝐵) that's distant from 𝑋 a multiple integer of 𝑇. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝐼 ∈ ℤ)    &   ⊢ (𝜑 → 𝐽 ∈ ℤ)    &   ⊢ (𝜑 → (𝑋 + (𝐼 · 𝑇)) ∈ (𝐴(,]𝐵))    &   ⊢ (𝜑 → (𝑋 + (𝐽 · 𝑇)) ∈ (𝐴(,]𝐵))    ⇒   ⊢ (𝜑 → 𝐼 = 𝐽)
Theorem	fourierdlem36 43574*	𝐹 is an isomorphism. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ Fin)    &   ⊢ (𝜑 → 𝐴 ⊆ ℝ)    &   ⊢ 𝐹 = (℩𝑓𝑓 Isom < , < ((0...𝑁), 𝐴))    &   ⊢ 𝑁 = ((♯‘𝐴) − 1)    ⇒   ⊢ (𝜑 → 𝐹 Isom < , < ((0...𝑁), 𝐴))
Theorem	fourierdlem37 43575*	𝐼 is a function that maps any real point to the point that in the partition that immediately precedes the corresponding periodic point in the interval. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇)))    &   ⊢ 𝐿 = (𝑦 ∈ (𝐴(,]𝐵) ↦ if(𝑦 = 𝐵, 𝐴, 𝑦))    &   ⊢ 𝐼 = (𝑥 ∈ ℝ ↦ sup({𝑖 ∈ (0..^𝑀) ∣ (𝑄‘𝑖) ≤ (𝐿‘(𝐸‘𝑥))}, ℝ, < ))    ⇒   ⊢ (𝜑 → (𝐼:ℝ⟶(0..^𝑀) ∧ (𝑥 ∈ ℝ → sup({𝑖 ∈ (0..^𝑀) ∣ (𝑄‘𝑖) ≤ (𝐿‘(𝐸‘𝑥))}, ℝ, < ) ∈ {𝑖 ∈ (0..^𝑀) ∣ (𝑄‘𝑖) ≤ (𝐿‘(𝐸‘𝑥))})))
Theorem	fourierdlem38 43576*	The function 𝐹 is continuous on every interval induced by the partition 𝑄. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹 ∈ (dom 𝐹–cn→ℂ))    &   ⊢ 𝑃 = (𝑛 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑛)) ∣ (((𝑝‘0) = -π ∧ (𝑝‘𝑛) = π) ∧ ∀𝑖 ∈ (0..^𝑛)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    &   ⊢ 𝐻 = (𝐴 ∪ ((-π[,]π) ∖ dom 𝐹))    &   ⊢ (𝜑 → ran 𝑄 = 𝐻)    ⇒   ⊢ ((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) → (𝐹 ↾ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))) ∈ (((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))–cn→ℂ))
Theorem	fourierdlem39 43577*	Integration by parts of ∫(𝐴(,)𝐵)((𝐹‘𝑥) · (sin‘(𝑅 · 𝑥))) d𝑥 (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 ≤ 𝐵)    &   ⊢ (𝜑 → 𝐹 ∈ ((𝐴[,]𝐵)–cn→ℂ))    &   ⊢ 𝐺 = (ℝ D 𝐹)    &   ⊢ (𝜑 → 𝐺 ∈ ((𝐴(,)𝐵)–cn→ℂ))    &   ⊢ (𝜑 → ∃𝑦 ∈ ℝ ∀𝑥 ∈ (𝐴(,)𝐵)(abs‘(𝐺‘𝑥)) ≤ 𝑦)    &   ⊢ (𝜑 → 𝑅 ∈ ℝ+)    ⇒   ⊢ (𝜑 → ∫(𝐴(,)𝐵)((𝐹‘𝑥) · (sin‘(𝑅 · 𝑥))) d𝑥 = ((((𝐹‘𝐵) · -((cos‘(𝑅 · 𝐵)) / 𝑅)) − ((𝐹‘𝐴) · -((cos‘(𝑅 · 𝐴)) / 𝑅))) − ∫(𝐴(,)𝐵)((𝐺‘𝑥) · -((cos‘(𝑅 · 𝑥)) / 𝑅)) d𝑥))
Theorem	fourierdlem40 43578*	𝐻 is a continuous function on any partition interval. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ (𝜑 → 𝐴 ∈ (-π[,]π))    &   ⊢ (𝜑 → 𝐵 ∈ (-π[,]π))    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → ¬ 0 ∈ (𝐴(,)𝐵))    &   ⊢ (𝜑 → (𝐹 ↾ ((𝐴 + 𝑋)(,)(𝐵 + 𝑋))) ∈ (((𝐴 + 𝑋)(,)(𝐵 + 𝑋))–cn→ℂ))    &   ⊢ (𝜑 → 𝑌 ∈ ℝ)    &   ⊢ (𝜑 → 𝑊 ∈ ℝ)    &   ⊢ 𝐻 = (𝑠 ∈ (-π[,]π) ↦ if(𝑠 = 0, 0, (((𝐹‘(𝑋 + 𝑠)) − if(0 < 𝑠, 𝑌, 𝑊)) / 𝑠)))    ⇒   ⊢ (𝜑 → (𝐻 ↾ (𝐴(,)𝐵)) ∈ ((𝐴(,)𝐵)–cn→ℂ))
Theorem	fourierdlem41 43579*	Lemma used to prove that every real is a limit point for the domain of the derivative of the periodic function to be approximated. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷 ∧ 𝑘 ∈ ℤ) → (𝑥 + (𝑘 · 𝑇)) ∈ 𝐷)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ 𝑍 = (𝑥 ∈ ℝ ↦ ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇))    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + (𝑍‘𝑥)))    &   ⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    &   ⊢ ((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) → ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1))) ⊆ 𝐷)    ⇒   ⊢ (𝜑 → (∃𝑦 ∈ ℝ (𝑦 < 𝑋 ∧ (𝑦(,)𝑋) ⊆ 𝐷) ∧ ∃𝑦 ∈ ℝ (𝑋 < 𝑦 ∧ (𝑋(,)𝑦) ⊆ 𝐷)))
Theorem	fourierdlem42 43580*	The set of points in a moved partition are finite. (Contributed by Glauco Siliprandi, 11-Dec-2019.) (Revised by AV, 29-Sep-2020.)
⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 < 𝐶)    &   ⊢ 𝑇 = (𝐶 − 𝐵)    &   ⊢ (𝜑 → 𝐴 ⊆ (𝐵[,]𝐶))    &   ⊢ (𝜑 → 𝐴 ∈ Fin)    &   ⊢ (𝜑 → 𝐵 ∈ 𝐴)    &   ⊢ (𝜑 → 𝐶 ∈ 𝐴)    &   ⊢ 𝐷 = (abs ∘ − )    &   ⊢ 𝐼 = ((𝐴 × 𝐴) ∖ I )    &   ⊢ 𝑅 = ran (𝐷 ↾ 𝐼)    &   ⊢ 𝐸 = inf(𝑅, ℝ, < )    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝑌 ∈ ℝ)    &   ⊢ 𝐽 = (topGen‘ran (,))    &   ⊢ 𝐾 = (𝐽 ↾t (𝑋[,]𝑌))    &   ⊢ 𝐻 = {𝑥 ∈ (𝑋[,]𝑌) ∣ ∃𝑘 ∈ ℤ (𝑥 + (𝑘 · 𝑇)) ∈ 𝐴}    &   ⊢ (𝜓 ↔ ((𝜑 ∧ (𝑎 ∈ ℝ ∧ 𝑏 ∈ ℝ ∧ 𝑎 < 𝑏)) ∧ ∃𝑗 ∈ ℤ ∃𝑘 ∈ ℤ ((𝑎 + (𝑗 · 𝑇)) ∈ 𝐴 ∧ (𝑏 + (𝑘 · 𝑇)) ∈ 𝐴)))    ⇒   ⊢ (𝜑 → 𝐻 ∈ Fin)
Theorem	fourierdlem43 43581	𝐾 is a real function. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐾 = (𝑠 ∈ (-π[,]π) ↦ if(𝑠 = 0, 1, (𝑠 / (2 · (sin‘(𝑠 / 2))))))    ⇒   ⊢ 𝐾:(-π[,]π)⟶ℝ
Theorem	fourierdlem44 43582	A condition for having (sin‘(𝐴 / 2)) nonzero. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ ((𝐴 ∈ (-π[,]π) ∧ 𝐴 ≠ 0) → (sin‘(𝐴 / 2)) ≠ 0)
Theorem	fourierdlem46 43583*	The function 𝐹 has a limit at the bounds of every interval induced by the partition 𝑄. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹 ∈ (dom 𝐹–cn→ℂ))    &   ⊢ ((𝜑 ∧ 𝑥 ∈ ((-π[,)π) ∖ dom 𝐹)) → ((𝐹 ↾ (𝑥(,)+∞)) limℂ 𝑥) ≠ ∅)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ ((-π(,]π) ∖ dom 𝐹)) → ((𝐹 ↾ (-∞(,)𝑥)) limℂ 𝑥) ≠ ∅)    &   ⊢ (𝜑 → 𝑄 Isom < , < ((0...𝑀), 𝐻))    &   ⊢ (𝜑 → 𝑄:(0...𝑀)⟶𝐻)    &   ⊢ (𝜑 → 𝐼 ∈ (0..^𝑀))    &   ⊢ (𝜑 → (𝑄‘𝐼) < (𝑄‘(𝐼 + 1)))    &   ⊢ (𝜑 → ((𝑄‘𝐼)(,)(𝑄‘(𝐼 + 1))) ⊆ (-π(,)π))    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ 𝐻 = ({-π, π, 𝐶} ∪ ((-π[,]π) ∖ dom 𝐹))    &   ⊢ (𝜑 → ran 𝑄 = 𝐻)    ⇒   ⊢ (𝜑 → (((𝐹 ↾ ((𝑄‘𝐼)(,)(𝑄‘(𝐼 + 1)))) limℂ (𝑄‘𝐼)) ≠ ∅ ∧ ((𝐹 ↾ ((𝑄‘𝐼)(,)(𝑄‘(𝐼 + 1)))) limℂ (𝑄‘(𝐼 + 1))) ≠ ∅))
Theorem	fourierdlem47 43584*	For 𝑟 large enough, the final expression is less than the given positive 𝐸. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → (𝑥 ∈ 𝐼 ↦ 𝐹) ∈ 𝐿1)    &   ⊢ ((𝜑 ∧ 𝑟 ∈ ℝ) → (𝑥 ∈ 𝐼 ↦ (𝐹 · -𝐺)) ∈ 𝐿1)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐼) → 𝐹 ∈ ℂ)    &   ⊢ (((𝜑 ∧ 𝑥 ∈ 𝐼) ∧ 𝑟 ∈ ℂ) → 𝐺 ∈ ℂ)    &   ⊢ (((𝜑 ∧ 𝑥 ∈ 𝐼) ∧ 𝑟 ∈ ℝ) → (abs‘𝐺) ≤ 1)    &   ⊢ (𝜑 → 𝐴 ∈ ℂ)    &   ⊢ 𝑋 = (abs‘𝐴)    &   ⊢ (𝜑 → 𝐶 ∈ ℂ)    &   ⊢ 𝑌 = (abs‘𝐶)    &   ⊢ 𝑍 = ∫𝐼(abs‘𝐹) d𝑥    &   ⊢ (𝜑 → 𝐸 ∈ ℝ+)    &   ⊢ ((𝜑 ∧ 𝑟 ∈ ℂ) → 𝐵 ∈ ℂ)    &   ⊢ ((𝜑 ∧ 𝑟 ∈ ℝ) → (abs‘𝐵) ≤ 1)    &   ⊢ ((𝜑 ∧ 𝑟 ∈ ℂ) → 𝐷 ∈ ℂ)    &   ⊢ ((𝜑 ∧ 𝑟 ∈ ℝ) → (abs‘𝐷) ≤ 1)    &   ⊢ 𝑀 = ((⌊‘((((𝑋 + 𝑌) + 𝑍) / 𝐸) + 1)) + 1)    ⇒   ⊢ (𝜑 → ∃𝑚 ∈ ℕ ∀𝑟 ∈ (𝑚(,)+∞)(abs‘(((𝐴 · -(𝐵 / 𝑟)) − (𝐶 · -(𝐷 / 𝑟))) − ∫𝐼(𝐹 · -(𝐺 / 𝑟)) d𝑥)) < 𝐸)
Theorem	fourierdlem48 43585*	The given periodic function 𝐹 has a right limit at every point in the reals. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    &   ⊢ (𝜑 → 𝐹:𝐷⟶ℝ)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷 ∧ 𝑘 ∈ ℤ) → (𝑥 + (𝑘 · 𝑇)) ∈ 𝐷)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷 ∧ 𝑘 ∈ ℤ) → (𝐹‘(𝑥 + (𝑘 · 𝑇))) = (𝐹‘𝑥))    &   ⊢ ((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) → (𝐹 ↾ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))) ∈ (((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))–cn→ℂ))    &   ⊢ ((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) → 𝑅 ∈ ((𝐹 ↾ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))) limℂ (𝑄‘𝑖)))    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ 𝑍 = (𝑥 ∈ ℝ ↦ ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇))    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + (𝑍‘𝑥)))    &   ⊢ (𝜒 ↔ ((((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) ∧ 𝑦 ∈ ((𝑄‘𝑖)[,)(𝑄‘(𝑖 + 1)))) ∧ 𝑘 ∈ ℤ) ∧ 𝑦 = (𝑋 + (𝑘 · 𝑇))))    ⇒   ⊢ (𝜑 → ((𝐹 ↾ (𝑋(,)+∞)) limℂ 𝑋) ≠ ∅)
Theorem	fourierdlem49 43586*	The given periodic function 𝐹 has a left limit at every point in the reals. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    &   ⊢ (𝜑 → 𝐷 ⊆ ℝ)    &   ⊢ (𝜑 → 𝐹:𝐷⟶ℝ)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷 ∧ 𝑘 ∈ ℤ) → (𝑥 + (𝑘 · 𝑇)) ∈ 𝐷)    &   ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷 ∧ 𝑘 ∈ ℤ) → (𝐹‘(𝑥 + (𝑘 · 𝑇))) = (𝐹‘𝑥))    &   ⊢ ((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) → (𝐹 ↾ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))) ∈ (((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))–cn→ℂ))    &   ⊢ ((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) → 𝐿 ∈ ((𝐹 ↾ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))) limℂ (𝑄‘(𝑖 + 1))))    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ 𝑍 = (𝑥 ∈ ℝ ↦ ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇))    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + (𝑍‘𝑥)))    ⇒   ⊢ (𝜑 → ((𝐹 ↾ (-∞(,)𝑋)) limℂ 𝑋) ≠ ∅)
Theorem	fourierdlem50 43587*	Continuity of 𝑂 and its limits with respect to the 𝑆 partition. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = (-π + 𝑋) ∧ (𝑝‘𝑚) = (π + 𝑋)) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑉 ∈ (𝑃‘𝑀))    &   ⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ (𝜑 → (𝐴[,]𝐵) ⊆ (-π[,]π))    &   ⊢ 𝑄 = (𝑖 ∈ (0...𝑀) ↦ ((𝑉‘𝑖) − 𝑋))    &   ⊢ 𝑇 = ({𝐴, 𝐵} ∪ (ran 𝑄 ∩ (𝐴(,)𝐵)))    &   ⊢ 𝑁 = ((♯‘𝑇) − 1)    &   ⊢ 𝑆 = (℩𝑓𝑓 Isom < , < ((0...𝑁), 𝑇))    &   ⊢ (𝜑 → 𝐽 ∈ (0..^𝑁))    &   ⊢ 𝑈 = (℩𝑖 ∈ (0..^𝑀)((𝑆‘𝐽)(,)(𝑆‘(𝐽 + 1))) ⊆ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1))))    &   ⊢ (𝜒 ↔ ((((𝜑 ∧ 𝑖 ∈ (0..^𝑀)) ∧ ((𝑆‘𝐽)(,)(𝑆‘(𝐽 + 1))) ⊆ ((𝑄‘𝑖)(,)(𝑄‘(𝑖 + 1)))) ∧ 𝑘 ∈ (0..^𝑀)) ∧ ((𝑆‘𝐽)(,)(𝑆‘(𝐽 + 1))) ⊆ ((𝑄‘𝑘)(,)(𝑄‘(𝑘 + 1)))))    ⇒   ⊢ (𝜑 → (𝑈 ∈ (0..^𝑀) ∧ ((𝑆‘𝐽)(,)(𝑆‘(𝐽 + 1))) ⊆ ((𝑄‘𝑈)(,)(𝑄‘(𝑈 + 1)))))
Theorem	fourierdlem51 43588*	𝑋 is in the periodic partition, when the considered interval is centered at 𝑋. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 0)    &   ⊢ (𝜑 → 0 < 𝐵)    &   ⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ (𝜑 → 𝐶 ∈ Fin)    &   ⊢ (𝜑 → 𝐶 ⊆ (𝐴[,]𝐵))    &   ⊢ (𝜑 → 𝐵 ∈ 𝐶)    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇)))    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → (𝐸‘𝑋) ∈ 𝐶)    &   ⊢ 𝐷 = ({(𝐴 + 𝑋), (𝐵 + 𝑋)} ∪ {𝑦 ∈ ((𝐴 + 𝑋)[,](𝐵 + 𝑋)) ∣ ∃𝑘 ∈ ℤ (𝑦 + (𝑘 · 𝑇)) ∈ 𝐶})    &   ⊢ 𝐹 = (℩𝑓𝑓 Isom < , < ((0...((♯‘𝐷) − 1)), 𝐷))    &   ⊢ 𝐻 = {𝑦 ∈ ((𝐴 + 𝑋)(,](𝐵 + 𝑋)) ∣ ∃𝑘 ∈ ℤ (𝑦 + (𝑘 · 𝑇)) ∈ 𝐶}    ⇒   ⊢ (𝜑 → 𝑋 ∈ ran 𝐹)
Theorem	fourierdlem52 43589*	d16:d17,d18:jca |- ( ph -> ( ( S 0) ≤ 𝐴 ∧ 𝐴 ≤ (𝑆 0 ) ) ) . (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝑇 ∈ Fin)    &   ⊢ 𝑁 = ((♯‘𝑇) − 1)    &   ⊢ 𝑆 = (℩𝑓𝑓 Isom < , < ((0...𝑁), 𝑇))    &   ⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝑇 ⊆ (𝐴[,]𝐵))    &   ⊢ (𝜑 → 𝐴 ∈ 𝑇)    &   ⊢ (𝜑 → 𝐵 ∈ 𝑇)    ⇒   ⊢ (𝜑 → ((𝑆:(0...𝑁)⟶(𝐴[,]𝐵) ∧ (𝑆‘0) = 𝐴) ∧ (𝑆‘𝑁) = 𝐵))
Theorem	fourierdlem53 43590*	The limit of 𝐹(𝑠) at (𝑋 + 𝐷) is the limit of 𝐹(𝑋 + 𝑠) at 𝐷. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 ⊆ ℝ)    &   ⊢ 𝐺 = (𝑠 ∈ 𝐴 ↦ (𝐹‘(𝑋 + 𝑠)))    &   ⊢ ((𝜑 ∧ 𝑠 ∈ 𝐴) → (𝑋 + 𝑠) ∈ 𝐵)    &   ⊢ (𝜑 → 𝐵 ⊆ ℝ)    &   ⊢ ((𝜑 ∧ 𝑠 ∈ 𝐴) → 𝑠 ≠ 𝐷)    &   ⊢ (𝜑 → 𝐶 ∈ ((𝐹 ↾ 𝐵) limℂ (𝑋 + 𝐷)))    &   ⊢ (𝜑 → 𝐷 ∈ ℂ)    ⇒   ⊢ (𝜑 → 𝐶 ∈ (𝐺 limℂ 𝐷))
Theorem	fourierdlem54 43591*	Given a partition 𝑄 and an arbitrary interval [𝐶, 𝐷], a partition 𝑆 on [𝐶, 𝐷] is built such that it preserves any periodic function piecewise continuous on 𝑄 will be piecewise continuous on 𝑆, with the same limits. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ (𝜑 → 𝐷 ∈ ℝ)    &   ⊢ (𝜑 → 𝐶 < 𝐷)    &   ⊢ 𝑂 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐶 ∧ (𝑝‘𝑚) = 𝐷) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ 𝐻 = ({𝐶, 𝐷} ∪ {𝑥 ∈ (𝐶[,]𝐷) ∣ ∃𝑘 ∈ ℤ (𝑥 + (𝑘 · 𝑇)) ∈ ran 𝑄})    &   ⊢ 𝑁 = ((♯‘𝐻) − 1)    &   ⊢ 𝑆 = (℩𝑓𝑓 Isom < , < ((0...𝑁), 𝐻))    ⇒   ⊢ (𝜑 → ((𝑁 ∈ ℕ ∧ 𝑆 ∈ (𝑂‘𝑁)) ∧ 𝑆 Isom < , < ((0...𝑁), 𝐻)))
Theorem	fourierdlem55 43592*	𝑈 is a real function. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝑌 ∈ ℝ)    &   ⊢ (𝜑 → 𝑊 ∈ ℝ)    &   ⊢ 𝐻 = (𝑠 ∈ (-π[,]π) ↦ if(𝑠 = 0, 0, (((𝐹‘(𝑋 + 𝑠)) − if(0 < 𝑠, 𝑌, 𝑊)) / 𝑠)))    &   ⊢ 𝐾 = (𝑠 ∈ (-π[,]π) ↦ if(𝑠 = 0, 1, (𝑠 / (2 · (sin‘(𝑠 / 2))))))    &   ⊢ 𝑈 = (𝑠 ∈ (-π[,]π) ↦ ((𝐻‘𝑠) · (𝐾‘𝑠)))    ⇒   ⊢ (𝜑 → 𝑈:(-π[,]π)⟶ℝ)
Theorem	fourierdlem56 43593*	Derivative of the 𝐾 function on an interval not containing ' 0 '. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐾 = (𝑠 ∈ (-π[,]π) ↦ if(𝑠 = 0, 1, (𝑠 / (2 · (sin‘(𝑠 / 2))))))    &   ⊢ (𝜑 → (𝐴(,)𝐵) ⊆ ((-π[,]π) ∖ {0}))    &   ⊢ ((𝜑 ∧ 𝑠 ∈ (𝐴(,)𝐵)) → 𝑠 ≠ 0)    ⇒   ⊢ (𝜑 → (ℝ D (𝑠 ∈ (𝐴(,)𝐵) ↦ (𝐾‘𝑠))) = (𝑠 ∈ (𝐴(,)𝐵) ↦ ((((sin‘(𝑠 / 2)) − (((cos‘(𝑠 / 2)) / 2) · 𝑠)) / ((sin‘(𝑠 / 2))↑2)) / 2)))
Theorem	fourierdlem57 43594*	The derivative of 𝑂. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → (ℝ D (𝐹 ↾ ((𝑋 + 𝐴)(,)(𝑋 + 𝐵)))):((𝑋 + 𝐴)(,)(𝑋 + 𝐵))⟶ℝ)    &   ⊢ (𝜑 → (𝐴(,)𝐵) ⊆ (-π[,]π))    &   ⊢ (𝜑 → ¬ 0 ∈ (𝐴(,)𝐵))    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ 𝑂 = (𝑠 ∈ (𝐴(,)𝐵) ↦ (((𝐹‘(𝑋 + 𝑠)) − 𝐶) / (2 · (sin‘(𝑠 / 2)))))    ⇒   ⊢ ((𝜑 → ((ℝ D 𝑂):(𝐴(,)𝐵)⟶ℝ ∧ (ℝ D 𝑂) = (𝑠 ∈ (𝐴(,)𝐵) ↦ (((((ℝ D (𝐹 ↾ ((𝑋 + 𝐴)(,)(𝑋 + 𝐵))))‘(𝑋 + 𝑠)) · (2 · (sin‘(𝑠 / 2)))) − ((cos‘(𝑠 / 2)) · ((𝐹‘(𝑋 + 𝑠)) − 𝐶))) / ((2 · (sin‘(𝑠 / 2)))↑2))))) ∧ (ℝ D (𝑠 ∈ (𝐴(,)𝐵) ↦ (2 · (sin‘(𝑠 / 2))))) = (𝑠 ∈ (𝐴(,)𝐵) ↦ (cos‘(𝑠 / 2))))
Theorem	fourierdlem58 43595*	The derivative of 𝐾 is continuous on the given interval. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐾 = (𝑠 ∈ 𝐴 ↦ (𝑠 / (2 · (sin‘(𝑠 / 2)))))    &   ⊢ (𝜑 → 𝐴 ⊆ (-π[,]π))    &   ⊢ (𝜑 → ¬ 0 ∈ 𝐴)    &   ⊢ (𝜑 → 𝐴 ∈ (topGen‘ran (,)))    ⇒   ⊢ (𝜑 → (ℝ D 𝐾) ∈ (𝐴–cn→ℝ))
Theorem	fourierdlem59 43596*	The derivative of 𝐻 is continuous on the given interval. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐹:ℝ⟶ℝ)    &   ⊢ (𝜑 → 𝑋 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → ¬ 0 ∈ (𝐴(,)𝐵))    &   ⊢ (𝜑 → (ℝ D (𝐹 ↾ ((𝑋 + 𝐴)(,)(𝑋 + 𝐵)))) ∈ (((𝑋 + 𝐴)(,)(𝑋 + 𝐵))–cn→ℝ))    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ 𝐻 = (𝑠 ∈ (𝐴(,)𝐵) ↦ (((𝐹‘(𝑋 + 𝑠)) − 𝐶) / 𝑠))    ⇒   ⊢ (𝜑 → (ℝ D 𝐻) ∈ ((𝐴(,)𝐵)–cn→ℝ))
Theorem	fourierdlem60 43597*	Given a differentiable function 𝐹, with finite limit of the derivative at 𝐴 the derived function 𝐻 has a limit at 0. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ (𝜑 → 𝐹:(𝐴(,)𝐵)⟶ℝ)    &   ⊢ (𝜑 → 𝑌 ∈ (𝐹 limℂ 𝐵))    &   ⊢ 𝐺 = (ℝ D 𝐹)    &   ⊢ (𝜑 → dom 𝐺 = (𝐴(,)𝐵))    &   ⊢ (𝜑 → 𝐸 ∈ (𝐺 limℂ 𝐵))    &   ⊢ 𝐻 = (𝑠 ∈ ((𝐴 − 𝐵)(,)0) ↦ (((𝐹‘(𝐵 + 𝑠)) − 𝑌) / 𝑠))    &   ⊢ 𝑁 = (𝑠 ∈ ((𝐴 − 𝐵)(,)0) ↦ ((𝐹‘(𝐵 + 𝑠)) − 𝑌))    &   ⊢ 𝐷 = (𝑠 ∈ ((𝐴 − 𝐵)(,)0) ↦ 𝑠)    ⇒   ⊢ (𝜑 → 𝐸 ∈ (𝐻 limℂ 0))
Theorem	fourierdlem61 43598*	Given a differentiable function 𝐹, with finite limit of the derivative at 𝐴 the derived function 𝐻 has a limit at 0. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ)    &   ⊢ (𝜑 → 𝐴 < 𝐵)    &   ⊢ (𝜑 → 𝐹:(𝐴(,)𝐵)⟶ℝ)    &   ⊢ (𝜑 → 𝑌 ∈ (𝐹 limℂ 𝐴))    &   ⊢ 𝐺 = (ℝ D 𝐹)    &   ⊢ (𝜑 → dom 𝐺 = (𝐴(,)𝐵))    &   ⊢ (𝜑 → 𝐸 ∈ (𝐺 limℂ 𝐴))    &   ⊢ 𝐻 = (𝑠 ∈ (0(,)(𝐵 − 𝐴)) ↦ (((𝐹‘(𝐴 + 𝑠)) − 𝑌) / 𝑠))    &   ⊢ 𝑁 = (𝑠 ∈ (0(,)(𝐵 − 𝐴)) ↦ ((𝐹‘(𝐴 + 𝑠)) − 𝑌))    &   ⊢ 𝐷 = (𝑠 ∈ (0(,)(𝐵 − 𝐴)) ↦ 𝑠)    ⇒   ⊢ (𝜑 → 𝐸 ∈ (𝐻 limℂ 0))
Theorem	fourierdlem62 43599	The function 𝐾 is continuous. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝐾 = (𝑦 ∈ (-π[,]π) ↦ if(𝑦 = 0, 1, (𝑦 / (2 · (sin‘(𝑦 / 2))))))    ⇒   ⊢ 𝐾 ∈ ((-π[,]π)–cn→ℝ)
Theorem	fourierdlem63 43600*	The upper bound of intervals in the moved partition are mapped to points that are not greater than the corresponding upper bounds in the original partition. (Contributed by Glauco Siliprandi, 11-Dec-2019.)
⊢ 𝑇 = (𝐵 − 𝐴)    &   ⊢ 𝑃 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐴 ∧ (𝑝‘𝑚) = 𝐵) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ (𝜑 → 𝑀 ∈ ℕ)    &   ⊢ (𝜑 → 𝑄 ∈ (𝑃‘𝑀))    &   ⊢ (𝜑 → 𝐶 ∈ ℝ)    &   ⊢ (𝜑 → 𝐷 ∈ ℝ)    &   ⊢ (𝜑 → 𝐶 < 𝐷)    &   ⊢ 𝑂 = (𝑚 ∈ ℕ ↦ {𝑝 ∈ (ℝ ↑m (0...𝑚)) ∣ (((𝑝‘0) = 𝐶 ∧ (𝑝‘𝑚) = 𝐷) ∧ ∀𝑖 ∈ (0..^𝑚)(𝑝‘𝑖) < (𝑝‘(𝑖 + 1)))})    &   ⊢ 𝐻 = ({𝐶, 𝐷} ∪ {𝑥 ∈ (𝐶[,]𝐷) ∣ ∃𝑘 ∈ ℤ (𝑥 + (𝑘 · 𝑇)) ∈ ran 𝑄})    &   ⊢ 𝑁 = ((♯‘𝐻) − 1)    &   ⊢ 𝑆 = (℩𝑓𝑓 Isom < , < ((0...𝑁), 𝐻))    &   ⊢ 𝐸 = (𝑥 ∈ ℝ ↦ (𝑥 + ((⌊‘((𝐵 − 𝑥) / 𝑇)) · 𝑇)))    &   ⊢ (𝜑 → 𝐾 ∈ (0...𝑀))    &   ⊢ (𝜑 → 𝐽 ∈ (0..^𝑁))    &   ⊢ (𝜑 → 𝑌 ∈ ((𝑆‘𝐽)[,)(𝑆‘(𝐽 + 1))))    &   ⊢ (𝜑 → (𝐸‘𝑌) < (𝑄‘𝐾))    &   ⊢ 𝑋 = ((𝑄‘𝐾) − ((𝐸‘𝑌) − 𝑌))    ⇒   ⊢ (𝜑 → (𝐸‘(𝑆‘(𝐽 + 1))) ≤ (𝑄‘𝐾))