P. 69 of Theorem List - Metamath Proof Explorer

Theorem List for Metamath Proof Explorer - 6801-6900   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	fin 6801	Mapping into an intersection. (Contributed by NM, 14-Sep-1999.) (Proof shortened by Andrew Salmon, 17-Sep-2011.)
⊢ (𝐹:𝐴⟶(𝐵 ∩ 𝐶) ↔ (𝐹:𝐴⟶𝐵 ∧ 𝐹:𝐴⟶𝐶))
Theorem	f0 6802	The empty function. (Contributed by NM, 14-Aug-1999.)
⊢ ∅:∅⟶𝐴
Theorem	f00 6803	A class is a function with empty codomain iff it and its domain are empty. (Contributed by NM, 10-Dec-2003.)
⊢ (𝐹:𝐴⟶∅ ↔ (𝐹 = ∅ ∧ 𝐴 = ∅))
Theorem	f0bi 6804	A function with empty domain is empty. (Contributed by Alexander van der Vekens, 30-Jun-2018.)
⊢ (𝐹:∅⟶𝑋 ↔ 𝐹 = ∅)
Theorem	f0dom0 6805	A function is empty iff it has an empty domain. (Contributed by AV, 10-Feb-2019.)
⊢ (𝐹:𝑋⟶𝑌 → (𝑋 = ∅ ↔ 𝐹 = ∅))
Theorem	f0rn0 6806*	If there is no element in the range of a function, its domain must be empty. (Contributed by Alexander van der Vekens, 12-Jul-2018.)
⊢ ((𝐸:𝑋⟶𝑌 ∧ ¬ ∃𝑦 ∈ 𝑌 𝑦 ∈ ran 𝐸) → 𝑋 = ∅)
Theorem	fconst 6807	A Cartesian product with a singleton is a constant function. (Contributed by NM, 14-Aug-1999.) (Proof shortened by Andrew Salmon, 17-Sep-2011.)
⊢ 𝐵 ∈ V    ⇒   ⊢ (𝐴 × {𝐵}):𝐴⟶{𝐵}
Theorem	fconstg 6808	A Cartesian product with a singleton is a constant function. (Contributed by NM, 19-Oct-2004.)
⊢ (𝐵 ∈ 𝑉 → (𝐴 × {𝐵}):𝐴⟶{𝐵})
Theorem	fnconstg 6809	A Cartesian product with a singleton is a constant function. (Contributed by NM, 24-Jul-2014.)
⊢ (𝐵 ∈ 𝑉 → (𝐴 × {𝐵}) Fn 𝐴)
Theorem	fconst6g 6810	Constant function with loose range. (Contributed by Stefan O'Rear, 1-Feb-2015.)
⊢ (𝐵 ∈ 𝐶 → (𝐴 × {𝐵}):𝐴⟶𝐶)
Theorem	fconst6 6811	A constant function as a mapping. (Contributed by Jeff Madsen, 30-Nov-2009.) (Revised by Mario Carneiro, 22-Apr-2015.)
⊢ 𝐵 ∈ 𝐶    ⇒   ⊢ (𝐴 × {𝐵}):𝐴⟶𝐶
Theorem	f1eq1 6812	Equality theorem for one-to-one functions. (Contributed by NM, 10-Feb-1997.)
⊢ (𝐹 = 𝐺 → (𝐹:𝐴–1-1→𝐵 ↔ 𝐺:𝐴–1-1→𝐵))
Theorem	f1eq2 6813	Equality theorem for one-to-one functions. (Contributed by NM, 10-Feb-1997.)
⊢ (𝐴 = 𝐵 → (𝐹:𝐴–1-1→𝐶 ↔ 𝐹:𝐵–1-1→𝐶))
Theorem	f1eq3 6814	Equality theorem for one-to-one functions. (Contributed by NM, 10-Feb-1997.)
⊢ (𝐴 = 𝐵 → (𝐹:𝐶–1-1→𝐴 ↔ 𝐹:𝐶–1-1→𝐵))
Theorem	nff1 6815	Bound-variable hypothesis builder for a one-to-one function. (Contributed by NM, 16-May-2004.)
⊢ Ⅎ𝑥𝐹    &   ⊢ Ⅎ𝑥𝐴    &   ⊢ Ⅎ𝑥𝐵    ⇒   ⊢ Ⅎ𝑥 𝐹:𝐴–1-1→𝐵
Theorem	dff12 6816*	Alternate definition of a one-to-one function. (Contributed by NM, 31-Dec-1996.)
⊢ (𝐹:𝐴–1-1→𝐵 ↔ (𝐹:𝐴⟶𝐵 ∧ ∀𝑦∃*𝑥 𝑥𝐹𝑦))
Theorem	f1f 6817	A one-to-one mapping is a mapping. (Contributed by NM, 31-Dec-1996.)
⊢ (𝐹:𝐴–1-1→𝐵 → 𝐹:𝐴⟶𝐵)
Theorem	f1fn 6818	A one-to-one mapping is a function on its domain. (Contributed by NM, 8-Mar-2014.)
⊢ (𝐹:𝐴–1-1→𝐵 → 𝐹 Fn 𝐴)
Theorem	f1fun 6819	A one-to-one mapping is a function. (Contributed by NM, 8-Mar-2014.)
⊢ (𝐹:𝐴–1-1→𝐵 → Fun 𝐹)
Theorem	f1rel 6820	A one-to-one onto mapping is a relation. (Contributed by NM, 8-Mar-2014.)
⊢ (𝐹:𝐴–1-1→𝐵 → Rel 𝐹)
Theorem	f1dm 6821	The domain of a one-to-one mapping. (Contributed by NM, 8-Mar-2014.) (Proof shortened by Wolf Lammen, 29-May-2024.)
⊢ (𝐹:𝐴–1-1→𝐵 → dom 𝐹 = 𝐴)
Theorem	f1ss 6822	A function that is one-to-one is also one-to-one on some superset of its codomain. (Contributed by Mario Carneiro, 12-Jan-2013.)
⊢ ((𝐹:𝐴–1-1→𝐵 ∧ 𝐵 ⊆ 𝐶) → 𝐹:𝐴–1-1→𝐶)
Theorem	f1ssr 6823	A function that is one-to-one is also one-to-one on some superset of its range. (Contributed by Stefan O'Rear, 20-Feb-2015.)
⊢ ((𝐹:𝐴–1-1→𝐵 ∧ ran 𝐹 ⊆ 𝐶) → 𝐹:𝐴–1-1→𝐶)
Theorem	f1ssres 6824	A function that is one-to-one is also one-to-one on any subclass of its domain. (Contributed by Mario Carneiro, 17-Jan-2015.)
⊢ ((𝐹:𝐴–1-1→𝐵 ∧ 𝐶 ⊆ 𝐴) → (𝐹 ↾ 𝐶):𝐶–1-1→𝐵)
Theorem	f1resf1 6825	The restriction of an injective function is injective. (Contributed by AV, 28-Jun-2022.)
⊢ ((𝐹:𝐴–1-1→𝐵 ∧ 𝐶 ⊆ 𝐴 ∧ (𝐹 ↾ 𝐶):𝐶⟶𝐷) → (𝐹 ↾ 𝐶):𝐶–1-1→𝐷)
Theorem	f1cnvcnv 6826	Two ways to express that a set 𝐴 (not necessarily a function) is one-to-one. Each side is equivalent to Definition 6.4(3) of [TakeutiZaring] p. 24, who use the notation "Un2 (A)" for one-to-one. We do not introduce a separate notation since we rarely use it. (Contributed by NM, 13-Aug-2004.)
⊢ (◡◡𝐴:dom 𝐴–1-1→V ↔ (Fun ◡𝐴 ∧ Fun ◡◡𝐴))
Theorem	f1cof1 6827	Composition of two one-to-one functions. Generalization of f1co 6828. (Contributed by AV, 18-Sep-2024.)
⊢ ((𝐹:𝐶–1-1→𝐷 ∧ 𝐺:𝐴–1-1→𝐵) → (𝐹 ∘ 𝐺):(◡𝐺 “ 𝐶)–1-1→𝐷)
Theorem	f1co 6828	Composition of one-to-one functions when the codomain of the first matches the domain of the second. Exercise 30 of [TakeutiZaring] p. 25. (Contributed by NM, 28-May-1998.) (Proof shortened by AV, 20-Sep-2024.)
⊢ ((𝐹:𝐵–1-1→𝐶 ∧ 𝐺:𝐴–1-1→𝐵) → (𝐹 ∘ 𝐺):𝐴–1-1→𝐶)
Theorem	f1coOLD 6829	Obsolete version of f1co 6828 as of 20-Sep-2024. (Contributed by NM, 28-May-1998.) (Proof modification is discouraged.) (New usage is discouraged.)
⊢ ((𝐹:𝐵–1-1→𝐶 ∧ 𝐺:𝐴–1-1→𝐵) → (𝐹 ∘ 𝐺):𝐴–1-1→𝐶)
Theorem	foeq1 6830	Equality theorem for onto functions. (Contributed by NM, 1-Aug-1994.)
⊢ (𝐹 = 𝐺 → (𝐹:𝐴–onto→𝐵 ↔ 𝐺:𝐴–onto→𝐵))
Theorem	foeq2 6831	Equality theorem for onto functions. (Contributed by NM, 1-Aug-1994.)
⊢ (𝐴 = 𝐵 → (𝐹:𝐴–onto→𝐶 ↔ 𝐹:𝐵–onto→𝐶))
Theorem	foeq3 6832	Equality theorem for onto functions. (Contributed by NM, 1-Aug-1994.)
⊢ (𝐴 = 𝐵 → (𝐹:𝐶–onto→𝐴 ↔ 𝐹:𝐶–onto→𝐵))
Theorem	nffo 6833	Bound-variable hypothesis builder for an onto function. (Contributed by NM, 16-May-2004.)
⊢ Ⅎ𝑥𝐹    &   ⊢ Ⅎ𝑥𝐴    &   ⊢ Ⅎ𝑥𝐵    ⇒   ⊢ Ⅎ𝑥 𝐹:𝐴–onto→𝐵
Theorem	fof 6834	An onto mapping is a mapping. (Contributed by NM, 3-Aug-1994.)
⊢ (𝐹:𝐴–onto→𝐵 → 𝐹:𝐴⟶𝐵)
Theorem	fofun 6835	An onto mapping is a function. (Contributed by NM, 29-Mar-2008.)
⊢ (𝐹:𝐴–onto→𝐵 → Fun 𝐹)
Theorem	fofn 6836	An onto mapping is a function on its domain. (Contributed by NM, 16-Dec-2008.)
⊢ (𝐹:𝐴–onto→𝐵 → 𝐹 Fn 𝐴)
Theorem	forn 6837	The codomain of an onto function is its range. (Contributed by NM, 3-Aug-1994.)
⊢ (𝐹:𝐴–onto→𝐵 → ran 𝐹 = 𝐵)
Theorem	dffo2 6838	Alternate definition of an onto function. (Contributed by NM, 22-Mar-2006.)
⊢ (𝐹:𝐴–onto→𝐵 ↔ (𝐹:𝐴⟶𝐵 ∧ ran 𝐹 = 𝐵))
Theorem	foima 6839	The image of the domain of an onto function. (Contributed by NM, 29-Nov-2002.)
⊢ (𝐹:𝐴–onto→𝐵 → (𝐹 “ 𝐴) = 𝐵)
Theorem	dffn4 6840	A function maps onto its range. (Contributed by NM, 10-May-1998.)
⊢ (𝐹 Fn 𝐴 ↔ 𝐹:𝐴–onto→ran 𝐹)
Theorem	funforn 6841	A function maps its domain onto its range. (Contributed by NM, 23-Jul-2004.)
⊢ (Fun 𝐴 ↔ 𝐴:dom 𝐴–onto→ran 𝐴)
Theorem	fodmrnu 6842	An onto function has unique domain and range. (Contributed by NM, 5-Nov-2006.)
⊢ ((𝐹:𝐴–onto→𝐵 ∧ 𝐹:𝐶–onto→𝐷) → (𝐴 = 𝐶 ∧ 𝐵 = 𝐷))
Theorem	fimadmfo 6843	A function is a function onto the image of its domain. (Contributed by AV, 1-Dec-2022.)
⊢ (𝐹:𝐴⟶𝐵 → 𝐹:𝐴–onto→(𝐹 “ 𝐴))
Theorem	fores 6844	Restriction of an onto function. (Contributed by NM, 4-Mar-1997.)
⊢ ((Fun 𝐹 ∧ 𝐴 ⊆ dom 𝐹) → (𝐹 ↾ 𝐴):𝐴–onto→(𝐹 “ 𝐴))
Theorem	fimadmfoALT 6845	Alternate proof of fimadmfo 6843, based on fores 6844. A function is a function onto the image of its domain. (Contributed by AV, 1-Dec-2022.) (Proof modification is discouraged.) (New usage is discouraged.)
⊢ (𝐹:𝐴⟶𝐵 → 𝐹:𝐴–onto→(𝐹 “ 𝐴))
Theorem	focnvimacdmdm 6846	The preimage of the codomain of a surjection is its domain. (Contributed by AV, 29-Sep-2024.)
⊢ (𝐺:𝐴–onto→𝐵 → (◡𝐺 “ 𝐵) = 𝐴)
Theorem	focofo 6847	Composition of onto functions. Generalisation of foco 6848. (Contributed by AV, 29-Sep-2024.)
⊢ ((𝐹:𝐴–onto→𝐵 ∧ Fun 𝐺 ∧ 𝐴 ⊆ ran 𝐺) → (𝐹 ∘ 𝐺):(◡𝐺 “ 𝐴)–onto→𝐵)
Theorem	foco 6848	Composition of onto functions. (Contributed by NM, 22-Mar-2006.) (Proof shortened by AV, 29-Sep-2024.)
⊢ ((𝐹:𝐵–onto→𝐶 ∧ 𝐺:𝐴–onto→𝐵) → (𝐹 ∘ 𝐺):𝐴–onto→𝐶)
Theorem	foconst 6849	A nonzero constant function is onto. (Contributed by NM, 12-Jan-2007.)
⊢ ((𝐹:𝐴⟶{𝐵} ∧ 𝐹 ≠ ∅) → 𝐹:𝐴–onto→{𝐵})
Theorem	f1oeq1 6850	Equality theorem for one-to-one onto functions. (Contributed by NM, 10-Feb-1997.)
⊢ (𝐹 = 𝐺 → (𝐹:𝐴–1-1-onto→𝐵 ↔ 𝐺:𝐴–1-1-onto→𝐵))
Theorem	f1oeq2 6851	Equality theorem for one-to-one onto functions. (Contributed by NM, 10-Feb-1997.)
⊢ (𝐴 = 𝐵 → (𝐹:𝐴–1-1-onto→𝐶 ↔ 𝐹:𝐵–1-1-onto→𝐶))
Theorem	f1oeq3 6852	Equality theorem for one-to-one onto functions. (Contributed by NM, 10-Feb-1997.)
⊢ (𝐴 = 𝐵 → (𝐹:𝐶–1-1-onto→𝐴 ↔ 𝐹:𝐶–1-1-onto→𝐵))
Theorem	f1oeq23 6853	Equality theorem for one-to-one onto functions. (Contributed by FL, 14-Jul-2012.)
⊢ ((𝐴 = 𝐵 ∧ 𝐶 = 𝐷) → (𝐹:𝐴–1-1-onto→𝐶 ↔ 𝐹:𝐵–1-1-onto→𝐷))
Theorem	f1eq123d 6854	Equality deduction for one-to-one functions. (Contributed by Mario Carneiro, 27-Jan-2017.)
⊢ (𝜑 → 𝐹 = 𝐺)    &   ⊢ (𝜑 → 𝐴 = 𝐵)    &   ⊢ (𝜑 → 𝐶 = 𝐷)    ⇒   ⊢ (𝜑 → (𝐹:𝐴–1-1→𝐶 ↔ 𝐺:𝐵–1-1→𝐷))
Theorem	foeq123d 6855	Equality deduction for onto functions. (Contributed by Mario Carneiro, 27-Jan-2017.)
⊢ (𝜑 → 𝐹 = 𝐺)    &   ⊢ (𝜑 → 𝐴 = 𝐵)    &   ⊢ (𝜑 → 𝐶 = 𝐷)    ⇒   ⊢ (𝜑 → (𝐹:𝐴–onto→𝐶 ↔ 𝐺:𝐵–onto→𝐷))
Theorem	f1oeq123d 6856	Equality deduction for one-to-one onto functions. (Contributed by Mario Carneiro, 27-Jan-2017.)
⊢ (𝜑 → 𝐹 = 𝐺)    &   ⊢ (𝜑 → 𝐴 = 𝐵)    &   ⊢ (𝜑 → 𝐶 = 𝐷)    ⇒   ⊢ (𝜑 → (𝐹:𝐴–1-1-onto→𝐶 ↔ 𝐺:𝐵–1-1-onto→𝐷))
Theorem	f1oeq1d 6857	Equality deduction for one-to-one onto functions. (Contributed by Glauco Siliprandi, 17-Aug-2020.)
⊢ (𝜑 → 𝐹 = 𝐺)    ⇒   ⊢ (𝜑 → (𝐹:𝐴–1-1-onto→𝐵 ↔ 𝐺:𝐴–1-1-onto→𝐵))
Theorem	f1oeq2d 6858	Equality deduction for one-to-one onto functions. (Contributed by Glauco Siliprandi, 17-Aug-2020.)
⊢ (𝜑 → 𝐴 = 𝐵)    ⇒   ⊢ (𝜑 → (𝐹:𝐴–1-1-onto→𝐶 ↔ 𝐹:𝐵–1-1-onto→𝐶))
Theorem	f1oeq3d 6859	Equality deduction for one-to-one onto functions. (Contributed by Glauco Siliprandi, 17-Aug-2020.)
⊢ (𝜑 → 𝐴 = 𝐵)    ⇒   ⊢ (𝜑 → (𝐹:𝐶–1-1-onto→𝐴 ↔ 𝐹:𝐶–1-1-onto→𝐵))
Theorem	nff1o 6860	Bound-variable hypothesis builder for a one-to-one onto function. (Contributed by NM, 16-May-2004.)
⊢ Ⅎ𝑥𝐹    &   ⊢ Ⅎ𝑥𝐴    &   ⊢ Ⅎ𝑥𝐵    ⇒   ⊢ Ⅎ𝑥 𝐹:𝐴–1-1-onto→𝐵
Theorem	f1of1 6861	A one-to-one onto mapping is a one-to-one mapping. (Contributed by NM, 12-Dec-2003.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → 𝐹:𝐴–1-1→𝐵)
Theorem	f1of 6862	A one-to-one onto mapping is a mapping. (Contributed by NM, 12-Dec-2003.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → 𝐹:𝐴⟶𝐵)
Theorem	f1ofn 6863	A one-to-one onto mapping is function on its domain. (Contributed by NM, 12-Dec-2003.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → 𝐹 Fn 𝐴)
Theorem	f1ofun 6864	A one-to-one onto mapping is a function. (Contributed by NM, 12-Dec-2003.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → Fun 𝐹)
Theorem	f1orel 6865	A one-to-one onto mapping is a relation. (Contributed by NM, 13-Dec-2003.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → Rel 𝐹)
Theorem	f1odm 6866	The domain of a one-to-one onto mapping. (Contributed by NM, 8-Mar-2014.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → dom 𝐹 = 𝐴)
Theorem	dff1o2 6867	Alternate definition of one-to-one onto function. (Contributed by NM, 10-Feb-1997.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 ↔ (𝐹 Fn 𝐴 ∧ Fun ◡𝐹 ∧ ran 𝐹 = 𝐵))
Theorem	dff1o3 6868	Alternate definition of one-to-one onto function. (Contributed by NM, 25-Mar-1998.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 ↔ (𝐹:𝐴–onto→𝐵 ∧ Fun ◡𝐹))
Theorem	f1ofo 6869	A one-to-one onto function is an onto function. (Contributed by NM, 28-Apr-2004.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → 𝐹:𝐴–onto→𝐵)
Theorem	dff1o4 6870	Alternate definition of one-to-one onto function. (Contributed by NM, 25-Mar-1998.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 ↔ (𝐹 Fn 𝐴 ∧ ◡𝐹 Fn 𝐵))
Theorem	dff1o5 6871	Alternate definition of one-to-one onto function. (Contributed by NM, 10-Dec-2003.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 ↔ (𝐹:𝐴–1-1→𝐵 ∧ ran 𝐹 = 𝐵))
Theorem	f1orn 6872	A one-to-one function maps onto its range. (Contributed by NM, 13-Aug-2004.)
⊢ (𝐹:𝐴–1-1-onto→ran 𝐹 ↔ (𝐹 Fn 𝐴 ∧ Fun ◡𝐹))
Theorem	f1f1orn 6873	A one-to-one function maps one-to-one onto its range. (Contributed by NM, 4-Sep-2004.)
⊢ (𝐹:𝐴–1-1→𝐵 → 𝐹:𝐴–1-1-onto→ran 𝐹)
Theorem	f1ocnv 6874	The converse of a one-to-one onto function is also one-to-one onto. (Contributed by NM, 11-Feb-1997.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → ◡𝐹:𝐵–1-1-onto→𝐴)
Theorem	f1ocnvb 6875	A relation is a one-to-one onto function iff its converse is a one-to-one onto function with domain and codomain/range interchanged. (Contributed by NM, 8-Dec-2003.)
⊢ (Rel 𝐹 → (𝐹:𝐴–1-1-onto→𝐵 ↔ ◡𝐹:𝐵–1-1-onto→𝐴))
Theorem	f1ores 6876	The restriction of a one-to-one function maps one-to-one onto the image. (Contributed by NM, 25-Mar-1998.)
⊢ ((𝐹:𝐴–1-1→𝐵 ∧ 𝐶 ⊆ 𝐴) → (𝐹 ↾ 𝐶):𝐶–1-1-onto→(𝐹 “ 𝐶))
Theorem	f1orescnv 6877	The converse of a one-to-one-onto restricted function. (Contributed by Paul Chapman, 21-Apr-2008.)
⊢ ((Fun ◡𝐹 ∧ (𝐹 ↾ 𝑅):𝑅–1-1-onto→𝑃) → (◡𝐹 ↾ 𝑃):𝑃–1-1-onto→𝑅)
Theorem	f1imacnv 6878	Preimage of an image. (Contributed by NM, 30-Sep-2004.)
⊢ ((𝐹:𝐴–1-1→𝐵 ∧ 𝐶 ⊆ 𝐴) → (◡𝐹 “ (𝐹 “ 𝐶)) = 𝐶)
Theorem	foimacnv 6879	A reverse version of f1imacnv 6878. (Contributed by Jeff Hankins, 16-Jul-2009.)
⊢ ((𝐹:𝐴–onto→𝐵 ∧ 𝐶 ⊆ 𝐵) → (𝐹 “ (◡𝐹 “ 𝐶)) = 𝐶)
Theorem	foun 6880	The union of two onto functions with disjoint domains is an onto function. (Contributed by Mario Carneiro, 22-Jun-2016.)
⊢ (((𝐹:𝐴–onto→𝐵 ∧ 𝐺:𝐶–onto→𝐷) ∧ (𝐴 ∩ 𝐶) = ∅) → (𝐹 ∪ 𝐺):(𝐴 ∪ 𝐶)–onto→(𝐵 ∪ 𝐷))
Theorem	f1oun 6881	The union of two one-to-one onto functions with disjoint domains and ranges. (Contributed by NM, 26-Mar-1998.)
⊢ (((𝐹:𝐴–1-1-onto→𝐵 ∧ 𝐺:𝐶–1-1-onto→𝐷) ∧ ((𝐴 ∩ 𝐶) = ∅ ∧ (𝐵 ∩ 𝐷) = ∅)) → (𝐹 ∪ 𝐺):(𝐴 ∪ 𝐶)–1-1-onto→(𝐵 ∪ 𝐷))
Theorem	f1un 6882	The union of two one-to-one functions with disjoint domains and codomains. (Contributed by BTernaryTau, 3-Dec-2024.)
⊢ (((𝐹:𝐴–1-1→𝐵 ∧ 𝐺:𝐶–1-1→𝐷) ∧ ((𝐴 ∩ 𝐶) = ∅ ∧ (𝐵 ∩ 𝐷) = ∅)) → (𝐹 ∪ 𝐺):(𝐴 ∪ 𝐶)–1-1→(𝐵 ∪ 𝐷))
Theorem	resdif 6883	The restriction of a one-to-one onto function to a difference maps onto the difference of the images. (Contributed by Paul Chapman, 11-Apr-2009.)
⊢ ((Fun ◡𝐹 ∧ (𝐹 ↾ 𝐴):𝐴–onto→𝐶 ∧ (𝐹 ↾ 𝐵):𝐵–onto→𝐷) → (𝐹 ↾ (𝐴 ∖ 𝐵)):(𝐴 ∖ 𝐵)–1-1-onto→(𝐶 ∖ 𝐷))
Theorem	resin 6884	The restriction of a one-to-one onto function to an intersection maps onto the intersection of the images. (Contributed by Paul Chapman, 11-Apr-2009.)
⊢ ((Fun ◡𝐹 ∧ (𝐹 ↾ 𝐴):𝐴–onto→𝐶 ∧ (𝐹 ↾ 𝐵):𝐵–onto→𝐷) → (𝐹 ↾ (𝐴 ∩ 𝐵)):(𝐴 ∩ 𝐵)–1-1-onto→(𝐶 ∩ 𝐷))
Theorem	f1oco 6885	Composition of one-to-one onto functions. (Contributed by NM, 19-Mar-1998.)
⊢ ((𝐹:𝐵–1-1-onto→𝐶 ∧ 𝐺:𝐴–1-1-onto→𝐵) → (𝐹 ∘ 𝐺):𝐴–1-1-onto→𝐶)
Theorem	f1cnv 6886	The converse of an injective function is bijective. (Contributed by FL, 11-Nov-2011.)
⊢ (𝐹:𝐴–1-1→𝐵 → ◡𝐹:ran 𝐹–1-1-onto→𝐴)
Theorem	funcocnv2 6887	Composition with the converse. (Contributed by Jeff Madsen, 2-Sep-2009.)
⊢ (Fun 𝐹 → (𝐹 ∘ ◡𝐹) = ( I ↾ ran 𝐹))
Theorem	fococnv2 6888	The composition of an onto function and its converse. (Contributed by Stefan O'Rear, 12-Feb-2015.)
⊢ (𝐹:𝐴–onto→𝐵 → (𝐹 ∘ ◡𝐹) = ( I ↾ 𝐵))
Theorem	f1ococnv2 6889	The composition of a one-to-one onto function and its converse equals the identity relation restricted to the function's range. (Contributed by NM, 13-Dec-2003.) (Proof shortened by Stefan O'Rear, 12-Feb-2015.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → (𝐹 ∘ ◡𝐹) = ( I ↾ 𝐵))
Theorem	f1cocnv2 6890	Composition of an injective function with its converse. (Contributed by FL, 11-Nov-2011.)
⊢ (𝐹:𝐴–1-1→𝐵 → (𝐹 ∘ ◡𝐹) = ( I ↾ ran 𝐹))
Theorem	f1ococnv1 6891	The composition of a one-to-one onto function's converse and itself equals the identity relation restricted to the function's domain. (Contributed by NM, 13-Dec-2003.)
⊢ (𝐹:𝐴–1-1-onto→𝐵 → (◡𝐹 ∘ 𝐹) = ( I ↾ 𝐴))
Theorem	f1cocnv1 6892	Composition of an injective function with its converse. (Contributed by FL, 11-Nov-2011.)
⊢ (𝐹:𝐴–1-1→𝐵 → (◡𝐹 ∘ 𝐹) = ( I ↾ 𝐴))
Theorem	funcoeqres 6893	Express a constraint on a composition as a constraint on the composand. (Contributed by Stefan O'Rear, 7-Mar-2015.)
⊢ ((Fun 𝐺 ∧ (𝐹 ∘ 𝐺) = 𝐻) → (𝐹 ↾ ran 𝐺) = (𝐻 ∘ ◡𝐺))
Theorem	f1ssf1 6894	A subset of an injective function is injective. (Contributed by AV, 20-Nov-2020.)
⊢ ((Fun 𝐹 ∧ Fun ◡𝐹 ∧ 𝐺 ⊆ 𝐹) → Fun ◡𝐺)
Theorem	f10 6895	The empty set maps one-to-one into any class. (Contributed by NM, 7-Apr-1998.)
⊢ ∅:∅–1-1→𝐴
Theorem	f10d 6896	The empty set maps one-to-one into any class, deduction version. (Contributed by AV, 25-Nov-2020.)
⊢ (𝜑 → 𝐹 = ∅)    ⇒   ⊢ (𝜑 → 𝐹:dom 𝐹–1-1→𝐴)
Theorem	f1o00 6897	One-to-one onto mapping of the empty set. (Contributed by NM, 15-Apr-1998.)
⊢ (𝐹:∅–1-1-onto→𝐴 ↔ (𝐹 = ∅ ∧ 𝐴 = ∅))
Theorem	fo00 6898	Onto mapping of the empty set. (Contributed by NM, 22-Mar-2006.)
⊢ (𝐹:∅–onto→𝐴 ↔ (𝐹 = ∅ ∧ 𝐴 = ∅))
Theorem	f1o0 6899	One-to-one onto mapping of the empty set. (Contributed by NM, 10-Sep-2004.)
⊢ ∅:∅–1-1-onto→∅
Theorem	f1oi 6900	A restriction of the identity relation is a one-to-one onto function. (Contributed by NM, 30-Apr-1998.) (Proof shortened by Andrew Salmon, 22-Oct-2011.)
⊢ ( I ↾ 𝐴):𝐴–1-1-onto→𝐴