P. 267 of Theorem List - Metamath Proof Explorer

Theorem List for Metamath Proof Explorer - 26601-26700   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	efif1olem4 26601*	The exponential function of an imaginary number maps any interval of length 2π one-to-one onto the unit circle. (Contributed by Paul Chapman, 16-Mar-2008.) (Proof shortened by Mario Carneiro, 13-May-2014.)
⊢ 𝐹 = (𝑤 ∈ 𝐷 ↦ (exp‘(i · 𝑤)))    &   ⊢ 𝐶 = (◡abs “ {1})    &   ⊢ (𝜑 → 𝐷 ⊆ ℝ)    &   ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐷 ∧ 𝑦 ∈ 𝐷)) → (abs‘(𝑥 − 𝑦)) < (2 · π))    &   ⊢ ((𝜑 ∧ 𝑧 ∈ ℝ) → ∃𝑦 ∈ 𝐷 ((𝑧 − 𝑦) / (2 · π)) ∈ ℤ)    &   ⊢ 𝑆 = (sin ↾ (-(π / 2)[,](π / 2)))    ⇒   ⊢ (𝜑 → 𝐹:𝐷–1-1-onto→𝐶)
Theorem	efif1o 26602*	The exponential function of an imaginary number maps any open-below, closed-above interval of length 2π one-to-one onto the unit circle. (Contributed by Paul Chapman, 16-Mar-2008.) (Revised by Mario Carneiro, 13-May-2014.)
⊢ 𝐹 = (𝑤 ∈ 𝐷 ↦ (exp‘(i · 𝑤)))    &   ⊢ 𝐶 = (◡abs “ {1})    &   ⊢ 𝐷 = (𝐴(,](𝐴 + (2 · π)))    ⇒   ⊢ (𝐴 ∈ ℝ → 𝐹:𝐷–1-1-onto→𝐶)
Theorem	efifo 26603*	The exponential function of an imaginary number maps the reals onto the unit circle. (Contributed by Mario Carneiro, 13-May-2014.)
⊢ 𝐹 = (𝑧 ∈ ℝ ↦ (exp‘(i · 𝑧)))    &   ⊢ 𝐶 = (◡abs “ {1})    ⇒   ⊢ 𝐹:ℝ–onto→𝐶
Theorem	eff1olem 26604*	The exponential function maps the set 𝑆, of complex numbers with imaginary part in a real interval of length 2 · π, one-to-one onto the nonzero complex numbers. (Contributed by Paul Chapman, 16-Apr-2008.) (Proof shortened by Mario Carneiro, 13-May-2014.)
⊢ 𝐹 = (𝑤 ∈ 𝐷 ↦ (exp‘(i · 𝑤)))    &   ⊢ 𝑆 = (◡ℑ “ 𝐷)    &   ⊢ (𝜑 → 𝐷 ⊆ ℝ)    &   ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐷 ∧ 𝑦 ∈ 𝐷)) → (abs‘(𝑥 − 𝑦)) < (2 · π))    &   ⊢ ((𝜑 ∧ 𝑧 ∈ ℝ) → ∃𝑦 ∈ 𝐷 ((𝑧 − 𝑦) / (2 · π)) ∈ ℤ)    ⇒   ⊢ (𝜑 → (exp ↾ 𝑆):𝑆–1-1-onto→(ℂ ∖ {0}))
Theorem	eff1o 26605	The exponential function maps the set 𝑆, of complex numbers with imaginary part in the closed-above, open-below interval from -π to π one-to-one onto the nonzero complex numbers. (Contributed by Paul Chapman, 16-Apr-2008.) (Revised by Mario Carneiro, 13-May-2014.)
⊢ 𝑆 = (◡ℑ “ (-π(,]π))    ⇒   ⊢ (exp ↾ 𝑆):𝑆–1-1-onto→(ℂ ∖ {0})
Theorem	efabl 26606*	The image of a subgroup of the group +, under the exponential function of a scaled complex number, is an Abelian group. (Contributed by Paul Chapman, 25-Apr-2008.) (Revised by Mario Carneiro, 12-May-2014.) (Revised by Thierry Arnoux, 26-Jan-2020.)
⊢ 𝐹 = (𝑥 ∈ 𝑋 ↦ (exp‘(𝐴 · 𝑥)))    &   ⊢ 𝐺 = ((mulGrp‘ℂfld) ↾s ran 𝐹)    &   ⊢ (𝜑 → 𝐴 ∈ ℂ)    &   ⊢ (𝜑 → 𝑋 ∈ (SubGrp‘ℂfld))    ⇒   ⊢ (𝜑 → 𝐺 ∈ Abel)
Theorem	efsubm 26607*	The image of a subgroup of the group +, under the exponential function of a scaled complex number is a submonoid of the multiplicative group of ℂfld. (Contributed by Thierry Arnoux, 26-Jan-2020.)
⊢ 𝐹 = (𝑥 ∈ 𝑋 ↦ (exp‘(𝐴 · 𝑥)))    &   ⊢ 𝐺 = ((mulGrp‘ℂfld) ↾s ran 𝐹)    &   ⊢ (𝜑 → 𝐴 ∈ ℂ)    &   ⊢ (𝜑 → 𝑋 ∈ (SubGrp‘ℂfld))    ⇒   ⊢ (𝜑 → ran 𝐹 ∈ (SubMnd‘(mulGrp‘ℂfld)))
Theorem	circgrp 26608	The circle group 𝑇 is an Abelian group. (Contributed by Paul Chapman, 25-Mar-2008.) (Revised by Mario Carneiro, 13-May-2014.) (Revised by Thierry Arnoux, 26-Jan-2020.)
⊢ 𝐶 = (◡abs “ {1})    &   ⊢ 𝑇 = ((mulGrp‘ℂfld) ↾s 𝐶)    ⇒   ⊢ 𝑇 ∈ Abel
Theorem	circsubm 26609	The circle group 𝑇 is a submonoid of the multiplicative group of ℂfld. (Contributed by Thierry Arnoux, 26-Jan-2020.)
⊢ 𝐶 = (◡abs “ {1})    &   ⊢ 𝑇 = ((mulGrp‘ℂfld) ↾s 𝐶)    ⇒   ⊢ 𝐶 ∈ (SubMnd‘(mulGrp‘ℂfld))
14.3.4  The natural logarithm on complex numbers
Syntax	clog 26610	Extend class notation with the natural logarithm function on complex numbers.
class log
Syntax	ccxp 26611	Extend class notation with the complex power function.
class ↑𝑐
Definition	df-log 26612	Define the natural logarithm function on complex numbers. It is defined as the principal value, that is, the inverse of the exponential whose imaginary part lies in the interval (-pi, pi]. See http://en.wikipedia.org/wiki/Natural_logarithm and https://en.wikipedia.org/wiki/Complex_logarithm. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ log = ◡(exp ↾ (◡ℑ “ (-π(,]π)))
Definition	df-cxp 26613*	Define the power function on complex numbers. Note that the value of this function when 𝑥 = 0 and (ℜ‘𝑦) ≤ 0, 𝑦 ≠ 0 should properly be undefined, but defining it by convention this way simplifies the domain. (Contributed by Mario Carneiro, 2-Aug-2014.)
⊢ ↑𝑐 = (𝑥 ∈ ℂ, 𝑦 ∈ ℂ ↦ if(𝑥 = 0, if(𝑦 = 0, 1, 0), (exp‘(𝑦 · (log‘𝑥)))))
Theorem	logrn 26614	The range of the natural logarithm function, also the principal domain of the exponential function. This allows to write the longer class expression as simply ran log. (Contributed by Paul Chapman, 21-Apr-2008.) (Revised by Mario Carneiro, 13-May-2014.)
⊢ ran log = (◡ℑ “ (-π(,]π))
Theorem	ellogrn 26615	Write out the property 𝐴 ∈ ran log explicitly. (Contributed by Mario Carneiro, 1-Apr-2015.)
⊢ (𝐴 ∈ ran log ↔ (𝐴 ∈ ℂ ∧ -π < (ℑ‘𝐴) ∧ (ℑ‘𝐴) ≤ π))
Theorem	dflog2 26616	The natural logarithm function in terms of the exponential function restricted to its principal domain. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ log = ◡(exp ↾ ran log)
Theorem	relogrn 26617	The range of the natural logarithm function includes the real numbers. (Contributed by Paul Chapman, 21-Apr-2008.) (Proof shortened by Mario Carneiro, 1-Apr-2015.)
⊢ (𝐴 ∈ ℝ → 𝐴 ∈ ran log)
Theorem	logrncn 26618	The range of the natural logarithm function is a subset of the complex numbers. (Contributed by Mario Carneiro, 13-May-2014.)
⊢ (𝐴 ∈ ran log → 𝐴 ∈ ℂ)
Theorem	eff1o2 26619	The exponential function restricted to its principal domain maps one-to-one onto the nonzero complex numbers. (Contributed by Paul Chapman, 21-Apr-2008.) (Revised by Mario Carneiro, 13-May-2014.)
⊢ (exp ↾ ran log):ran log–1-1-onto→(ℂ ∖ {0})
Theorem	logf1o 26620	The natural logarithm function maps the nonzero complex numbers one-to-one onto its range. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ log:(ℂ ∖ {0})–1-1-onto→ran log
Theorem	dfrelog 26621	The natural logarithm function on the positive reals in terms of the real exponential function. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ (log ↾ ℝ+) = ◡(exp ↾ ℝ)
Theorem	relogf1o 26622	The natural logarithm function maps the positive reals one-to-one onto the real numbers. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ (log ↾ ℝ+):ℝ+–1-1-onto→ℝ
Theorem	logrncl 26623	Closure of the natural logarithm function. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (log‘𝐴) ∈ ran log)
Theorem	logcl 26624	Closure of the natural logarithm function. (Contributed by NM, 21-Apr-2008.) (Revised by Mario Carneiro, 23-Sep-2014.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (log‘𝐴) ∈ ℂ)
Theorem	logimcl 26625	Closure of the imaginary part of the logarithm function. (Contributed by Mario Carneiro, 23-Sep-2014.) (Revised by Mario Carneiro, 1-Apr-2015.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (-π < (ℑ‘(log‘𝐴)) ∧ (ℑ‘(log‘𝐴)) ≤ π))
Theorem	logcld 26626	The logarithm of a nonzero complex number is a complex number. Deduction form of logcl 26624. (Contributed by David Moews, 28-Feb-2017.)
⊢ (𝜑 → 𝑋 ∈ ℂ)    &   ⊢ (𝜑 → 𝑋 ≠ 0)    ⇒   ⊢ (𝜑 → (log‘𝑋) ∈ ℂ)
Theorem	logimcld 26627	The imaginary part of the logarithm is in (-π(,]π). Deduction form of logimcl 26625. Compare logimclad 26628. (Contributed by David Moews, 28-Feb-2017.)
⊢ (𝜑 → 𝑋 ∈ ℂ)    &   ⊢ (𝜑 → 𝑋 ≠ 0)    ⇒   ⊢ (𝜑 → (-π < (ℑ‘(log‘𝑋)) ∧ (ℑ‘(log‘𝑋)) ≤ π))
Theorem	logimclad 26628	The imaginary part of the logarithm is in (-π(,]π). Alternate form of logimcld 26627. (Contributed by David Moews, 28-Feb-2017.)
⊢ (𝜑 → 𝑋 ∈ ℂ)    &   ⊢ (𝜑 → 𝑋 ≠ 0)    ⇒   ⊢ (𝜑 → (ℑ‘(log‘𝑋)) ∈ (-π(,]π))
Theorem	abslogimle 26629	The imaginary part of the logarithm function has absolute value less than pi. (Contributed by Mario Carneiro, 3-Jul-2017.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (abs‘(ℑ‘(log‘𝐴))) ≤ π)
Theorem	logrnaddcl 26630	The range of the natural logarithm is closed under addition with reals. (Contributed by Mario Carneiro, 3-Apr-2015.)
⊢ ((𝐴 ∈ ran log ∧ 𝐵 ∈ ℝ) → (𝐴 + 𝐵) ∈ ran log)
Theorem	relogcl 26631	Closure of the natural logarithm function on positive reals. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ (𝐴 ∈ ℝ+ → (log‘𝐴) ∈ ℝ)
Theorem	eflog 26632	Relationship between the natural logarithm function and the exponential function. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (exp‘(log‘𝐴)) = 𝐴)
Theorem	logeq0im1 26633	If the logarithm of a number is 0, the number must be 1. (Contributed by David A. Wheeler, 22-Jul-2017.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0 ∧ (log‘𝐴) = 0) → 𝐴 = 1)
Theorem	logccne0 26634	The logarithm isn't 0 if its argument isn't 0 or 1. (Contributed by David A. Wheeler, 17-Jul-2017.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0 ∧ 𝐴 ≠ 1) → (log‘𝐴) ≠ 0)
Theorem	logne0 26635	Logarithm of a non-1 positive real number is not zero and thus suitable as a divisor. (Contributed by Stefan O'Rear, 19-Sep-2014.) (Proof shortened by AV, 14-Jun-2020.)
⊢ ((𝐴 ∈ ℝ+ ∧ 𝐴 ≠ 1) → (log‘𝐴) ≠ 0)
Theorem	reeflog 26636	Relationship between the natural logarithm function and the exponential function. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ (𝐴 ∈ ℝ+ → (exp‘(log‘𝐴)) = 𝐴)
Theorem	logef 26637	Relationship between the natural logarithm function and the exponential function. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ (𝐴 ∈ ran log → (log‘(exp‘𝐴)) = 𝐴)
Theorem	relogef 26638	Relationship between the natural logarithm function and the exponential function. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ (𝐴 ∈ ℝ → (log‘(exp‘𝐴)) = 𝐴)
Theorem	logeftb 26639	Relationship between the natural logarithm function and the exponential function. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0 ∧ 𝐵 ∈ ran log) → ((log‘𝐴) = 𝐵 ↔ (exp‘𝐵) = 𝐴))
Theorem	relogeftb 26640	Relationship between the natural logarithm function and the exponential function. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ ((𝐴 ∈ ℝ+ ∧ 𝐵 ∈ ℝ) → ((log‘𝐴) = 𝐵 ↔ (exp‘𝐵) = 𝐴))
Theorem	log1 26641	The natural logarithm of 1. One case of Property 1a of [Cohen] p. 301. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ (log‘1) = 0
Theorem	loge 26642	The natural logarithm of e. One case of Property 1b of [Cohen] p. 301. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ (log‘e) = 1
Theorem	logi 26643	The natural logarithm of i. (Contributed by Scott Fenton, 13-Apr-2020.)
⊢ (log‘i) = (i · (π / 2))
Theorem	logneg 26644	The natural logarithm of a negative real number. (Contributed by Mario Carneiro, 13-May-2014.) (Revised by Mario Carneiro, 3-Apr-2015.)
⊢ (𝐴 ∈ ℝ+ → (log‘-𝐴) = ((log‘𝐴) + (i · π)))
Theorem	logm1 26645	The natural logarithm of negative 1. (Contributed by Paul Chapman, 21-Apr-2008.) (Revised by Mario Carneiro, 13-May-2014.)
⊢ (log‘-1) = (i · π)
Theorem	lognegb 26646	If a number has imaginary part equal to π, then it is on the negative real axis and vice-versa. (Contributed by Mario Carneiro, 23-Sep-2014.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (-𝐴 ∈ ℝ+ ↔ (ℑ‘(log‘𝐴)) = π))
Theorem	relogoprlem 26647	Lemma for relogmul 26648 and relogdiv 26649. Remark of [Cohen] p. 301 ("The proof of Property 3 is quite similar to the proof given for Property 2"). (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ (((log‘𝐴) ∈ ℂ ∧ (log‘𝐵) ∈ ℂ) → (exp‘((log‘𝐴)𝐹(log‘𝐵))) = ((exp‘(log‘𝐴))𝐺(exp‘(log‘𝐵))))    &   ⊢ (((log‘𝐴) ∈ ℝ ∧ (log‘𝐵) ∈ ℝ) → ((log‘𝐴)𝐹(log‘𝐵)) ∈ ℝ)    ⇒   ⊢ ((𝐴 ∈ ℝ+ ∧ 𝐵 ∈ ℝ+) → (log‘(𝐴𝐺𝐵)) = ((log‘𝐴)𝐹(log‘𝐵)))
Theorem	relogmul 26648	The natural logarithm of the product of two positive real numbers is the sum of natural logarithms. Property 2 of [Cohen] p. 301, restricted to natural logarithms. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ ((𝐴 ∈ ℝ+ ∧ 𝐵 ∈ ℝ+) → (log‘(𝐴 · 𝐵)) = ((log‘𝐴) + (log‘𝐵)))
Theorem	relogdiv 26649	The natural logarithm of the quotient of two positive real numbers is the difference of natural logarithms. Exercise 72(a) and Property 3 of [Cohen] p. 301, restricted to natural logarithms. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ ((𝐴 ∈ ℝ+ ∧ 𝐵 ∈ ℝ+) → (log‘(𝐴 / 𝐵)) = ((log‘𝐴) − (log‘𝐵)))
Theorem	explog 26650	Exponentiation of a nonzero complex number to an integer power. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0 ∧ 𝑁 ∈ ℤ) → (𝐴↑𝑁) = (exp‘(𝑁 · (log‘𝐴))))
Theorem	reexplog 26651	Exponentiation of a positive real number to an integer power. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ ((𝐴 ∈ ℝ+ ∧ 𝑁 ∈ ℤ) → (𝐴↑𝑁) = (exp‘(𝑁 · (log‘𝐴))))
Theorem	relogexp 26652	The natural logarithm of positive 𝐴 raised to an integer power. Property 4 of [Cohen] p. 301-302, restricted to natural logarithms and integer powers 𝑁. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ ((𝐴 ∈ ℝ+ ∧ 𝑁 ∈ ℤ) → (log‘(𝐴↑𝑁)) = (𝑁 · (log‘𝐴)))
Theorem	relog 26653	Real part of a logarithm. (Contributed by Mario Carneiro, 15-Sep-2014.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (ℜ‘(log‘𝐴)) = (log‘(abs‘𝐴)))
Theorem	relogiso 26654	The natural logarithm function on positive reals determines an isomorphism from the positive reals onto the reals. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ (log ↾ ℝ+) Isom < , < (ℝ+, ℝ)
Theorem	reloggim 26655	The natural logarithm is a group isomorphism from the group of positive reals under multiplication to the group of reals under addition. (Contributed by Mario Carneiro, 21-Jun-2015.) (Revised by Thierry Arnoux, 30-Jun-2019.)
⊢ 𝑃 = ((mulGrp‘ℂfld) ↾s ℝ+)    ⇒   ⊢ (log ↾ ℝ+) ∈ (𝑃 GrpIso ℝfld)
Theorem	logltb 26656	The natural logarithm function on positive reals is strictly monotonic. (Contributed by Steve Rodriguez, 25-Nov-2007.)
⊢ ((𝐴 ∈ ℝ+ ∧ 𝐵 ∈ ℝ+) → (𝐴 < 𝐵 ↔ (log‘𝐴) < (log‘𝐵)))
Theorem	logfac 26657*	The logarithm of a factorial can be expressed as a finite sum of logs. (Contributed by Mario Carneiro, 17-Apr-2015.)
⊢ (𝑁 ∈ ℕ0 → (log‘(!‘𝑁)) = Σ𝑘 ∈ (1...𝑁)(log‘𝑘))
Theorem	eflogeq 26658*	Solve an equation involving an exponential. (Contributed by Mario Carneiro, 23-Apr-2015.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐵 ∈ ℂ ∧ 𝐵 ≠ 0) → ((exp‘𝐴) = 𝐵 ↔ ∃𝑛 ∈ ℤ 𝐴 = ((log‘𝐵) + ((i · (2 · π)) · 𝑛))))
Theorem	logleb 26659	Natural logarithm preserves ≤. (Contributed by Stefan O'Rear, 19-Sep-2014.)
⊢ ((𝐴 ∈ ℝ+ ∧ 𝐵 ∈ ℝ+) → (𝐴 ≤ 𝐵 ↔ (log‘𝐴) ≤ (log‘𝐵)))
Theorem	rplogcl 26660	Closure of the logarithm function in the positive reals. (Contributed by Mario Carneiro, 21-Sep-2014.)
⊢ ((𝐴 ∈ ℝ ∧ 1 < 𝐴) → (log‘𝐴) ∈ ℝ+)
Theorem	logge0 26661	The logarithm of a number greater than 1 is nonnegative. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ ((𝐴 ∈ ℝ ∧ 1 ≤ 𝐴) → 0 ≤ (log‘𝐴))
Theorem	logcj 26662	The natural logarithm distributes under conjugation away from the branch cut. (Contributed by Mario Carneiro, 25-Feb-2015.)
⊢ ((𝐴 ∈ ℂ ∧ (ℑ‘𝐴) ≠ 0) → (log‘(∗‘𝐴)) = (∗‘(log‘𝐴)))
Theorem	efiarg 26663	The exponential of the "arg" function ℑ ∘ log. (Contributed by Mario Carneiro, 25-Feb-2015.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (exp‘(i · (ℑ‘(log‘𝐴)))) = (𝐴 / (abs‘𝐴)))
Theorem	cosargd 26664	The cosine of the argument is the quotient of the real part and the absolute value. Compare to efiarg 26663. (Contributed by David Moews, 28-Feb-2017.)
⊢ (𝜑 → 𝑋 ∈ ℂ)    &   ⊢ (𝜑 → 𝑋 ≠ 0)    ⇒   ⊢ (𝜑 → (cos‘(ℑ‘(log‘𝑋))) = ((ℜ‘𝑋) / (abs‘𝑋)))
Theorem	cosarg0d 26665	The cosine of the argument is zero precisely on the imaginary axis. (Contributed by David Moews, 28-Feb-2017.)
⊢ (𝜑 → 𝑋 ∈ ℂ)    &   ⊢ (𝜑 → 𝑋 ≠ 0)    ⇒   ⊢ (𝜑 → ((cos‘(ℑ‘(log‘𝑋))) = 0 ↔ (ℜ‘𝑋) = 0))
Theorem	argregt0 26666	Closure of the argument of a complex number with positive real part. (Contributed by Mario Carneiro, 25-Feb-2015.)
⊢ ((𝐴 ∈ ℂ ∧ 0 < (ℜ‘𝐴)) → (ℑ‘(log‘𝐴)) ∈ (-(π / 2)(,)(π / 2)))
Theorem	argrege0 26667	Closure of the argument of a complex number with nonnegative real part. (Contributed by Mario Carneiro, 2-Apr-2015.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0 ∧ 0 ≤ (ℜ‘𝐴)) → (ℑ‘(log‘𝐴)) ∈ (-(π / 2)[,](π / 2)))
Theorem	argimgt0 26668	Closure of the argument of a complex number with positive imaginary part. (Contributed by Mario Carneiro, 25-Feb-2015.)
⊢ ((𝐴 ∈ ℂ ∧ 0 < (ℑ‘𝐴)) → (ℑ‘(log‘𝐴)) ∈ (0(,)π))
Theorem	argimlt0 26669	Closure of the argument of a complex number with negative imaginary part. (Contributed by Mario Carneiro, 25-Feb-2015.)
⊢ ((𝐴 ∈ ℂ ∧ (ℑ‘𝐴) < 0) → (ℑ‘(log‘𝐴)) ∈ (-π(,)0))
Theorem	logimul 26670	Multiplying a number by i increases the logarithm of the number by iπ / 2. (Contributed by Mario Carneiro, 4-Apr-2015.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0 ∧ 0 ≤ (ℜ‘𝐴)) → (log‘(i · 𝐴)) = ((log‘𝐴) + (i · (π / 2))))
Theorem	logneg2 26671	The logarithm of the negative of a number with positive imaginary part is i · π less than the original. (Compare logneg 26644.) (Contributed by Mario Carneiro, 3-Apr-2015.)
⊢ ((𝐴 ∈ ℂ ∧ 0 < (ℑ‘𝐴)) → (log‘-𝐴) = ((log‘𝐴) − (i · π)))
Theorem	logmul2 26672	Generalization of relogmul 26648 to a complex left argument. (Contributed by Mario Carneiro, 9-Jul-2017.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0 ∧ 𝐵 ∈ ℝ+) → (log‘(𝐴 · 𝐵)) = ((log‘𝐴) + (log‘𝐵)))
Theorem	logdiv2 26673	Generalization of relogdiv 26649 to a complex left argument. (Contributed by Mario Carneiro, 8-Jul-2017.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0 ∧ 𝐵 ∈ ℝ+) → (log‘(𝐴 / 𝐵)) = ((log‘𝐴) − (log‘𝐵)))
Theorem	abslogle 26674	Bound on the magnitude of the complex logarithm function. (Contributed by Mario Carneiro, 3-Jul-2017.)
⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ≠ 0) → (abs‘(log‘𝐴)) ≤ ((abs‘(log‘(abs‘𝐴))) + π))
Theorem	tanarg 26675	The basic relation between the "arg" function ℑ ∘ log and the arctangent. (Contributed by Mario Carneiro, 25-Feb-2015.)
⊢ ((𝐴 ∈ ℂ ∧ (ℜ‘𝐴) ≠ 0) → (tan‘(ℑ‘(log‘𝐴))) = ((ℑ‘𝐴) / (ℜ‘𝐴)))
Theorem	logdivlti 26676	The log𝑥 / 𝑥 function is strictly decreasing on the reals greater than e. (Contributed by Mario Carneiro, 14-Mar-2014.)
⊢ (((𝐴 ∈ ℝ ∧ 𝐵 ∈ ℝ ∧ e ≤ 𝐴) ∧ 𝐴 < 𝐵) → ((log‘𝐵) / 𝐵) < ((log‘𝐴) / 𝐴))
Theorem	logdivlt 26677	The log𝑥 / 𝑥 function is strictly decreasing on the reals greater than e. (Contributed by Mario Carneiro, 14-Mar-2014.)
⊢ (((𝐴 ∈ ℝ ∧ e ≤ 𝐴) ∧ (𝐵 ∈ ℝ ∧ e ≤ 𝐵)) → (𝐴 < 𝐵 ↔ ((log‘𝐵) / 𝐵) < ((log‘𝐴) / 𝐴)))
Theorem	logdivle 26678	The log𝑥 / 𝑥 function is strictly decreasing on the reals greater than e. (Contributed by Mario Carneiro, 3-May-2016.)
⊢ (((𝐴 ∈ ℝ ∧ e ≤ 𝐴) ∧ (𝐵 ∈ ℝ ∧ e ≤ 𝐵)) → (𝐴 ≤ 𝐵 ↔ ((log‘𝐵) / 𝐵) ≤ ((log‘𝐴) / 𝐴)))
Theorem	relogcld 26679	Closure of the natural logarithm function. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ (𝜑 → 𝐴 ∈ ℝ+)    ⇒   ⊢ (𝜑 → (log‘𝐴) ∈ ℝ)
Theorem	reeflogd 26680	Relationship between the natural logarithm function and the exponential function. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ (𝜑 → 𝐴 ∈ ℝ+)    ⇒   ⊢ (𝜑 → (exp‘(log‘𝐴)) = 𝐴)
Theorem	relogmuld 26681	The natural logarithm of the product of two positive real numbers is the sum of natural logarithms. Property 2 of [Cohen] p. 301, restricted to natural logarithms. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ (𝜑 → 𝐴 ∈ ℝ+)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ+)    ⇒   ⊢ (𝜑 → (log‘(𝐴 · 𝐵)) = ((log‘𝐴) + (log‘𝐵)))
Theorem	relogdivd 26682	The natural logarithm of the quotient of two positive real numbers is the difference of natural logarithms. Exercise 72(a) and Property 3 of [Cohen] p. 301, restricted to natural logarithms. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ (𝜑 → 𝐴 ∈ ℝ+)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ+)    ⇒   ⊢ (𝜑 → (log‘(𝐴 / 𝐵)) = ((log‘𝐴) − (log‘𝐵)))
Theorem	logled 26683	Natural logarithm preserves ≤. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ (𝜑 → 𝐴 ∈ ℝ+)    &   ⊢ (𝜑 → 𝐵 ∈ ℝ+)    ⇒   ⊢ (𝜑 → (𝐴 ≤ 𝐵 ↔ (log‘𝐴) ≤ (log‘𝐵)))
Theorem	relogefd 26684	Relationship between the natural logarithm function and the exponential function. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    ⇒   ⊢ (𝜑 → (log‘(exp‘𝐴)) = 𝐴)
Theorem	rplogcld 26685	Closure of the logarithm function in the positive reals. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 1 < 𝐴)    ⇒   ⊢ (𝜑 → (log‘𝐴) ∈ ℝ+)
Theorem	logge0d 26686	The logarithm of a number greater than 1 is nonnegative. (Contributed by Mario Carneiro, 29-May-2016.)
⊢ (𝜑 → 𝐴 ∈ ℝ)    &   ⊢ (𝜑 → 1 ≤ 𝐴)    ⇒   ⊢ (𝜑 → 0 ≤ (log‘𝐴))
Theorem	logge0b 26687	The logarithm of a number is nonnegative iff the number is greater than or equal to 1. (Contributed by AV, 30-May-2020.)
⊢ (𝐴 ∈ ℝ+ → (0 ≤ (log‘𝐴) ↔ 1 ≤ 𝐴))
Theorem	loggt0b 26688	The logarithm of a number is positive iff the number is greater than 1. (Contributed by AV, 30-May-2020.)
⊢ (𝐴 ∈ ℝ+ → (0 < (log‘𝐴) ↔ 1 < 𝐴))
Theorem	logle1b 26689	The logarithm of a number is less than or equal to 1 iff the number is less than or equal to Euler's constant. (Contributed by AV, 30-May-2020.)
⊢ (𝐴 ∈ ℝ+ → ((log‘𝐴) ≤ 1 ↔ 𝐴 ≤ e))
Theorem	loglt1b 26690	The logarithm of a number is less than 1 iff the number is less than Euler's constant. (Contributed by AV, 30-May-2020.)
⊢ (𝐴 ∈ ℝ+ → ((log‘𝐴) < 1 ↔ 𝐴 < e))
Theorem	divlogrlim 26691	The inverse logarithm function converges to zero. (Contributed by Mario Carneiro, 30-May-2016.)
⊢ (𝑥 ∈ (1(,)+∞) ↦ (1 / (log‘𝑥))) ⇝𝑟 0
Theorem	logno1 26692	The logarithm function is not eventually bounded. (Contributed by Mario Carneiro, 30-Apr-2016.) (Proof shortened by Mario Carneiro, 30-May-2016.)
⊢ ¬ (𝑥 ∈ ℝ+ ↦ (log‘𝑥)) ∈ 𝑂(1)
Theorem	dvrelog 26693	The derivative of the real logarithm function. (Contributed by Mario Carneiro, 24-Feb-2015.)
⊢ (ℝ D (log ↾ ℝ+)) = (𝑥 ∈ ℝ+ ↦ (1 / 𝑥))
Theorem	relogcn 26694	The real logarithm function is continuous. (Contributed by Mario Carneiro, 17-Feb-2015.)
⊢ (log ↾ ℝ+) ∈ (ℝ+–cn→ℝ)
Theorem	ellogdm 26695	Elementhood in the "continuous domain" of the complex logarithm. (Contributed by Mario Carneiro, 18-Feb-2015.)
⊢ 𝐷 = (ℂ ∖ (-∞(,]0))    ⇒   ⊢ (𝐴 ∈ 𝐷 ↔ (𝐴 ∈ ℂ ∧ (𝐴 ∈ ℝ → 𝐴 ∈ ℝ+)))
Theorem	logdmn0 26696	A number in the continuous domain of log is nonzero. (Contributed by Mario Carneiro, 18-Feb-2015.)
⊢ 𝐷 = (ℂ ∖ (-∞(,]0))    ⇒   ⊢ (𝐴 ∈ 𝐷 → 𝐴 ≠ 0)
Theorem	logdmnrp 26697	A number in the continuous domain of log is not a strictly negative number. (Contributed by Mario Carneiro, 18-Feb-2015.)
⊢ 𝐷 = (ℂ ∖ (-∞(,]0))    ⇒   ⊢ (𝐴 ∈ 𝐷 → ¬ -𝐴 ∈ ℝ+)
Theorem	logdmss 26698	The continuity domain of log is a subset of the regular domain of log. (Contributed by Mario Carneiro, 1-Mar-2015.)
⊢ 𝐷 = (ℂ ∖ (-∞(,]0))    ⇒   ⊢ 𝐷 ⊆ (ℂ ∖ {0})
Theorem	logcnlem2 26699	Lemma for logcn 26703. (Contributed by Mario Carneiro, 25-Feb-2015.)
⊢ 𝐷 = (ℂ ∖ (-∞(,]0))    &   ⊢ 𝑆 = if(𝐴 ∈ ℝ+, 𝐴, (abs‘(ℑ‘𝐴)))    &   ⊢ 𝑇 = ((abs‘𝐴) · (𝑅 / (1 + 𝑅)))    &   ⊢ (𝜑 → 𝐴 ∈ 𝐷)    &   ⊢ (𝜑 → 𝑅 ∈ ℝ+)    ⇒   ⊢ (𝜑 → if(𝑆 ≤ 𝑇, 𝑆, 𝑇) ∈ ℝ+)
Theorem	logcnlem3 26700	Lemma for logcn 26703. (Contributed by Mario Carneiro, 25-Feb-2015.)
⊢ 𝐷 = (ℂ ∖ (-∞(,]0))    &   ⊢ 𝑆 = if(𝐴 ∈ ℝ+, 𝐴, (abs‘(ℑ‘𝐴)))    &   ⊢ 𝑇 = ((abs‘𝐴) · (𝑅 / (1 + 𝑅)))    &   ⊢ (𝜑 → 𝐴 ∈ 𝐷)    &   ⊢ (𝜑 → 𝑅 ∈ ℝ+)    &   ⊢ (𝜑 → 𝐵 ∈ 𝐷)    &   ⊢ (𝜑 → (abs‘(𝐴 − 𝐵)) < if(𝑆 ≤ 𝑇, 𝑆, 𝑇))    ⇒   ⊢ (𝜑 → (-π < ((ℑ‘(log‘𝐵)) − (ℑ‘(log‘𝐴))) ∧ ((ℑ‘(log‘𝐵)) − (ℑ‘(log‘𝐴))) ≤ π))