P. 162 of Theorem List - Intuitionistic Logic Explorer

Theorem List for Intuitionistic Logic Explorer - 16101-16200   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	umgrnloopv 16101	In a multigraph, there is no loop, i.e. no edge connecting a vertex with itself. (Contributed by Alexander van der Vekens, 26-Jan-2018.) (Revised by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   =>    |- ( ( G e. UMGraph /\ M e. W ) -> ( ( E ` X ) = { M , N } -> M =/= N ) )
Theorem	umgredgprv 16102	In a multigraph, an edge is an unordered pair of vertices. This theorem would not hold for arbitrary hyper-/pseudographs since either M or N could be proper classes ( ( E ` X ) would be a loop in this case), which are no vertices of course. (Contributed by Alexander van der Vekens, 19-Aug-2017.) (Revised by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   &    |- V = (Vtx ` G )   =>    |- ( ( G e. UMGraph /\ X e. dom E ) -> ( ( E ` X ) = { M , N } -> ( M e. V /\ N e. V ) ) )
Theorem	umgrnloop 16103*	In a multigraph, there is no loop, i.e. no edge connecting a vertex with itself. (Contributed by Alexander van der Vekens, 19-Aug-2017.) (Revised by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   =>    |- ( G e. UMGraph -> ( E. x e. dom E ( E ` x ) = { M , N } -> M =/= N ) )
Theorem	umgrnloop0 16104*	A multigraph has no loops. (Contributed by Alexander van der Vekens, 6-Dec-2017.) (Revised by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   =>    |- ( G e. UMGraph -> { x e. dom E | ( E ` x ) = { U } } = (/) )
Theorem	umgr0e 16105	The empty graph, with vertices but no edges, is a multigraph. (Contributed by Mario Carneiro, 12-Mar-2015.) (Revised by AV, 25-Nov-2020.)
|- ( ph -> G e. W )   &    |- ( ph -> (iEdg ` G ) = (/) )   =>    |- ( ph -> G e. UMGraph )
Theorem	upgr0e 16106	The empty graph, with vertices but no edges, is a pseudograph. (Contributed by Mario Carneiro, 12-Mar-2015.) (Revised by AV, 11-Oct-2020.) (Proof shortened by AV, 25-Nov-2020.)
|- ( ph -> G e. W )   &    |- ( ph -> (iEdg ` G ) = (/) )   =>    |- ( ph -> G e. UPGraph )
Theorem	upgr1elem1 16107*	Lemma for upgr1edc 16108. (Contributed by AV, 16-Oct-2020.) (Revised by Jim Kingdon, 6-Jan-2026.)
|- ( ph -> { B , C } e. S )   &    |- ( ph -> B e. W )   &    |- ( ph -> C e. X )   &    |- ( ph -> DECID B = C )   =>    |- ( ph -> { { B , C } } C_ { x e. S | ( x ~~ 1o \/ x ~~ 2o ) } )
Theorem	upgr1edc 16108	A pseudograph with one edge. Such a graph is actually a simple pseudograph. (Contributed by Mario Carneiro, 12-Mar-2015.) (Revised by AV, 16-Oct-2020.) (Revised by AV, 21-Mar-2021.) (Proof shortened by AV, 17-Apr-2021.)
|- V = (Vtx ` G )   &    |- ( ph -> A e. X )   &    |- ( ph -> B e. V )   &    |- ( ph -> C e. V )   &    |- ( ph -> DECID B = C )   &    |- ( ph -> (iEdg ` G ) = { <. A , { B , C } >. } )   =>    |- ( ph -> G e. UPGraph )
Theorem	upgr0eop 16109	The empty graph, with vertices but no edges, is a pseudograph. The empty graph is actually a simple graph, and therefore also a multigraph ( G e. UMGraph). (Contributed by Mario Carneiro, 12-Mar-2015.) (Revised by AV, 11-Oct-2020.)
|- ( V e. W -> <. V , (/) >. e. UPGraph )
Theorem	upgr1eopdc 16110	A pseudograph with one edge. Such a graph is actually a simple pseudograph. (Contributed by Mario Carneiro, 12-Mar-2015.) (Revised by AV, 10-Oct-2020.)
|- ( ph -> V e. W )   &    |- ( ph -> A e. X )   &    |- ( ph -> B e. V )   &    |- ( ph -> C e. V )   &    |- ( ph -> DECID B = C )   =>    |- ( ph -> <. V , { <. A , { B , C } >. } >. e. UPGraph )
Theorem	upgr1een 16111	A graph with one non-loop edge is a pseudograph. Variation of upgr1edc 16108 for a different way of specifying a graph with one edge. (Contributed by Jim Kingdon, 18-Mar-2026.)
|- ( ph -> K e. X )   &    |- ( ph -> V e. Y )   &    |- ( ph -> E e. ~P V )   &    |- ( ph -> E ~~ 2o )   =>    |- ( ph -> <. V , { <. K , E >. } >. e. UPGraph )
Theorem	umgr1een 16112	A graph with one non-loop edge is a multigraph. (Contributed by Jim Kingdon, 18-Mar-2026.)
|- ( ph -> K e. X )   &    |- ( ph -> V e. Y )   &    |- ( ph -> E e. ~P V )   &    |- ( ph -> E ~~ 2o )   =>    |- ( ph -> <. V , { <. K , E >. } >. e. UMGraph )
Theorem	upgrun 16113	The union U of two pseudographs G and H with the same vertex set V is a pseudograph with the vertex V and the union ( E u. F ) of the (indexed) edges. (Contributed by AV, 12-Oct-2020.) (Revised by AV, 24-Oct-2021.)
|- ( ph -> G e. UPGraph )   &    |- ( ph -> H e. UPGraph )   &    |- E = (iEdg ` G )   &    |- F = (iEdg ` H )   &    |- V = (Vtx ` G )   &    |- ( ph -> (Vtx ` H ) = V )   &    |- ( ph -> ( dom E i^i dom F ) = (/) )   &    |- ( ph -> U e. W )   &    |- ( ph -> (Vtx ` U ) = V )   &    |- ( ph -> (iEdg ` U ) = ( E u. F ) )   =>    |- ( ph -> U e. UPGraph )
Theorem	upgrunop 16114	The union of two pseudographs (with the same vertex set): If <. V , E >. and <. V , F >. are pseudographs, then <. V , E u. F >. is a pseudograph (the vertex set stays the same, but the edges from both graphs are kept). (Contributed by Mario Carneiro, 12-Mar-2015.) (Revised by AV, 12-Oct-2020.) (Revised by AV, 24-Oct-2021.)
|- ( ph -> G e. UPGraph )   &    |- ( ph -> H e. UPGraph )   &    |- E = (iEdg ` G )   &    |- F = (iEdg ` H )   &    |- V = (Vtx ` G )   &    |- ( ph -> (Vtx ` H ) = V )   &    |- ( ph -> ( dom E i^i dom F ) = (/) )   =>    |- ( ph -> <. V , ( E u. F ) >. e. UPGraph )
Theorem	umgrun 16115	The union U of two multigraphs G and H with the same vertex set V is a multigraph with the vertex V and the union ( E u. F ) of the (indexed) edges. (Contributed by AV, 25-Nov-2020.)
|- ( ph -> G e. UMGraph )   &    |- ( ph -> H e. UMGraph )   &    |- E = (iEdg ` G )   &    |- F = (iEdg ` H )   &    |- V = (Vtx ` G )   &    |- ( ph -> (Vtx ` H ) = V )   &    |- ( ph -> ( dom E i^i dom F ) = (/) )   &    |- ( ph -> U e. W )   &    |- ( ph -> (Vtx ` U ) = V )   &    |- ( ph -> (iEdg ` U ) = ( E u. F ) )   =>    |- ( ph -> U e. UMGraph )
Theorem	umgrunop 16116	The union of two multigraphs (with the same vertex set): If <. V , E >. and <. V , F >. are multigraphs, then <. V , E u. F >. is a multigraph (the vertex set stays the same, but the edges from both graphs are kept). (Contributed by Mario Carneiro, 12-Mar-2015.) (Revised by AV, 25-Nov-2020.)
|- ( ph -> G e. UMGraph )   &    |- ( ph -> H e. UMGraph )   &    |- E = (iEdg ` G )   &    |- F = (iEdg ` H )   &    |- V = (Vtx ` G )   &    |- ( ph -> (Vtx ` H ) = V )   &    |- ( ph -> ( dom E i^i dom F ) = (/) )   =>    |- ( ph -> <. V , ( E u. F ) >. e. UMGraph )
12.2.3  Loop-free graphs For a hypergraph, the property to be "loop-free" is expressed by I : dom I --> E with E = { x e. ~P V | 2o ~<_ x } and I = (iEdg ` G ). E is the set of edges which connect at least two vertices.
Theorem	umgrislfupgrenlem 16117	Lemma for umgrislfupgrdom 16118. (Contributed by AV, 27-Jan-2021.)
|- ( { x e. ~P V | ( x ~~ 1o \/ x ~~ 2o ) } i^i { x e. ~P V | 2o ~<_ x } ) = { x e. ~P V | x ~~ 2o }
Theorem	umgrislfupgrdom 16118*	A multigraph is a loop-free pseudograph. (Contributed by AV, 27-Jan-2021.)
|- V = (Vtx ` G )   &    |- I = (iEdg ` G )   =>    |- ( G e. UMGraph <-> ( G e. UPGraph /\ I : dom I --> { x e. ~P V | 2o ~<_ x } ) )
Theorem	lfgredg2dom 16119*	An edge of a loop-free graph has at least two ends. (Contributed by AV, 23-Feb-2021.)
|- I = (iEdg ` G )   &    |- A = dom I   &    |- E = { x e. ~P V | 2o ~<_ x }   =>    |- ( ( I : A --> E /\ X e. A ) -> 2o ~<_ ( I ` X ) )
Theorem	lfgrnloopen 16120*	A loop-free graph has no loops. (Contributed by AV, 23-Feb-2021.)
|- I = (iEdg ` G )   &    |- A = dom I   &    |- E = { x e. ~P V | 2o ~<_ x }   =>    |- ( I : A --> E -> { x e. A | ( I ` x ) ~~ 1o } = (/) )
12.2.4  Edges as subsets of vertices of graphs
Theorem	uhgredgiedgb 16121*	In a hypergraph, a set is an edge iff it is an indexed edge. (Contributed by AV, 17-Oct-2020.)
|- I = (iEdg ` G )   =>    |- ( G e. UHGraph -> ( E e. (Edg ` G ) <-> E. x e. dom I E = ( I ` x ) ) )
Theorem	uhgriedg0edg0 16122	A hypergraph has no edges iff its edge function is empty. (Contributed by AV, 21-Oct-2020.) (Proof shortened by AV, 8-Dec-2021.)
|- ( G e. UHGraph -> ( (Edg ` G ) = (/) <-> (iEdg ` G ) = (/) ) )
Theorem	uhgredgm 16123*	An edge of a hypergraph is an inhabited subset of vertices. (Contributed by AV, 28-Nov-2020.)
|- ( ( G e. UHGraph /\ E e. (Edg ` G ) ) -> ( E e. ~P (Vtx ` G ) /\ E. x x e. E ) )
Theorem	edguhgr 16124	An edge of a hypergraph is a subset of vertices. (Contributed by AV, 26-Oct-2020.) (Proof shortened by AV, 28-Nov-2020.)
|- ( ( G e. UHGraph /\ E e. (Edg ` G ) ) -> E e. ~P (Vtx ` G ) )
Theorem	uhgredgrnv 16125	An edge of a hypergraph contains only vertices. (Contributed by Alexander van der Vekens, 18-Feb-2018.) (Revised by AV, 4-Jun-2021.)
|- ( ( G e. UHGraph /\ E e. (Edg ` G ) /\ N e. E ) -> N e. (Vtx ` G ) )
Theorem	upgredgssen 16126*	The set of edges of a pseudograph is a subset of the set of unordered pairs of vertices. (Contributed by AV, 29-Nov-2020.)
|- ( G e. UPGraph -> (Edg ` G ) C_ { x e. ~P (Vtx ` G ) | ( x ~~ 1o \/ x ~~ 2o ) } )
Theorem	umgredgssen 16127*	The set of edges of a multigraph is a subset of the set of proper unordered pairs of vertices. (Contributed by AV, 25-Nov-2020.)
|- ( G e. UMGraph -> (Edg ` G ) C_ { x e. ~P (Vtx ` G ) | x ~~ 2o } )
Theorem	edgupgren 16128	Properties of an edge of a pseudograph. (Contributed by AV, 8-Nov-2020.)
|- ( ( G e. UPGraph /\ E e. (Edg ` G ) ) -> ( E e. ~P (Vtx ` G ) /\ ( E ~~ 1o \/ E ~~ 2o ) ) )
Theorem	edgumgren 16129	Properties of an edge of a multigraph. (Contributed by AV, 25-Nov-2020.)
|- ( ( G e. UMGraph /\ E e. (Edg ` G ) ) -> ( E e. ~P (Vtx ` G ) /\ E ~~ 2o ) )
Theorem	uhgrvtxedgiedgb 16130*	In a hypergraph, a vertex is incident with an edge iff it is contained in an element of the range of the edge function. (Contributed by AV, 24-Dec-2020.) (Revised by AV, 6-Jul-2022.)
|- I = (iEdg ` G )   &    |- E = (Edg ` G )   =>    |- ( ( G e. UHGraph /\ U e. V ) -> ( E. i e. dom I U e. ( I ` i ) <-> E. e e. E U e. e ) )
Theorem	upgredg 16131*	For each edge in a pseudograph, there are two vertices which are connected by this edge. (Contributed by AV, 4-Nov-2020.) (Proof shortened by AV, 26-Nov-2021.)
|- V = (Vtx ` G )   &    |- E = (Edg ` G )   =>    |- ( ( G e. UPGraph /\ C e. E ) -> E. a e. V E. b e. V C = { a , b } )
Theorem	umgredg 16132*	For each edge in a multigraph, there are two distinct vertices which are connected by this edge. (Contributed by Alexander van der Vekens, 9-Dec-2017.) (Revised by AV, 25-Nov-2020.)
|- V = (Vtx ` G )   &    |- E = (Edg ` G )   =>    |- ( ( G e. UMGraph /\ C e. E ) -> E. a e. V E. b e. V ( a =/= b /\ C = { a , b } ) )
Theorem	upgrpredgv 16133	An edge of a pseudograph always connects two vertices if the edge contains two sets. The two vertices/sets need not necessarily be different (loops are allowed). (Contributed by AV, 18-Nov-2021.)
|- V = (Vtx ` G )   &    |- E = (Edg ` G )   =>    |- ( ( G e. UPGraph /\ ( M e. U /\ N e. W ) /\ { M , N } e. E ) -> ( M e. V /\ N e. V ) )
Theorem	umgrpredgv 16134	An edge of a multigraph always connects two vertices. This theorem does not hold for arbitrary pseudographs: if either M or N is a proper class, then { M , N } e. E could still hold ( { M , N } would be either { M } or { N }, see prprc1 3799 or prprc2 3800, i.e. a loop), but M e. V or N e. V would not be true. (Contributed by AV, 27-Nov-2020.)
|- V = (Vtx ` G )   &    |- E = (Edg ` G )   =>    |- ( ( G e. UMGraph /\ { M , N } e. E ) -> ( M e. V /\ N e. V ) )
Theorem	upgredg2vtx 16135*	For a vertex incident to an edge there is another vertex incident to the edge in a pseudograph. (Contributed by AV, 18-Oct-2020.) (Revised by AV, 5-Dec-2020.)
|- V = (Vtx ` G )   &    |- E = (Edg ` G )   =>    |- ( ( G e. UPGraph /\ C e. E /\ A e. C ) -> E. b e. V C = { A , b } )
Theorem	upgredgpr 16136	If a proper pair (of vertices) is a subset of an edge in a pseudograph, the pair is the edge. (Contributed by AV, 30-Dec-2020.)
|- V = (Vtx ` G )   &    |- E = (Edg ` G )   =>    |- ( ( ( G e. UPGraph /\ C e. E /\ { A , B } C_ C ) /\ ( A e. U /\ B e. W /\ A =/= B ) ) -> { A , B } = C )
Theorem	umgredgne 16137	An edge of a multigraph always connects two different vertices. Analogue of umgrnloopv 16101. (Contributed by AV, 27-Nov-2020.)
|- E = (Edg ` G )   =>    |- ( ( G e. UMGraph /\ { M , N } e. E ) -> M =/= N )
Theorem	umgrnloop2 16138	A multigraph has no loops. (Contributed by AV, 27-Oct-2020.) (Revised by AV, 30-Nov-2020.)
|- ( G e. UMGraph -> { N , N } e/ (Edg ` G ) )
Theorem	umgredgnlp 16139*	An edge of a multigraph is not a loop. (Contributed by AV, 9-Jan-2020.) (Revised by AV, 8-Jun-2021.)
|- E = (Edg ` G )   =>    |- ( ( G e. UMGraph /\ C e. E ) -> -. E. v C = { v } )
12.2.5  Undirected simple graphs In this section, "simple graph" will always stand for "undirected simple graph (without loops)" and "simple pseudograph" for "undirected simple pseudograph (which could have loops)".
Syntax	cuspgr 16140	Extend class notation with undirected simple pseudographs (which could have loops).
class USPGraph
Syntax	cusgr 16141	Extend class notation with undirected simple graphs (without loops).
class USGraph
Definition	df-uspgren 16142*	Define the class of all undirected simple pseudographs (which could have loops). An undirected simple pseudograph is a special undirected pseudograph or a special undirected simple hypergraph, consisting of a set v (of "vertices") and an injective (one-to-one) function e (representing (indexed) "edges") into subsets of v of cardinality one or two, representing the two vertices incident to the edge, or the one vertex if the edge is a loop. In contrast to a pseudograph, there is at most one edge between two vertices resp. at most one loop for a vertex. (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by Jim Kingdon, 15-Jan-2026.)
|- USPGraph = { g | [. (Vtx ` g ) / v ]. [. (iEdg ` g ) / e ]. e : dom e -1-1-> { x e. ~P v | ( x ~~ 1o \/ x ~~ 2o ) } }
Definition	df-usgren 16143*	Define the class of all undirected simple graphs (without loops). An undirected simple graph is a special undirected simple pseudograph, consisting of a set v (of "vertices") and an injective (one-to-one) function e (representing (indexed) "edges") into subsets of v of cardinality two, representing the two vertices incident to the edge. In contrast to an undirected simple pseudograph, an undirected simple graph has no loops (edges connecting a vertex with itself). (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by AV, 13-Oct-2020.)
|- USGraph = { g | [. (Vtx ` g ) / v ]. [. (iEdg ` g ) / e ]. e : dom e -1-1-> { x e. ~P v | x ~~ 2o } }
Theorem	isuspgren 16144*	The property of being a simple pseudograph. (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by AV, 13-Oct-2020.)
|- V = (Vtx ` G )   &    |- E = (iEdg ` G )   =>    |- ( G e. U -> ( G e. USPGraph <-> E : dom E -1-1-> { x e. ~P V | ( x ~~ 1o \/ x ~~ 2o ) } ) )
Theorem	isusgren 16145*	The property of being a simple graph. (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by AV, 13-Oct-2020.)
|- V = (Vtx ` G )   &    |- E = (iEdg ` G )   =>    |- ( G e. U -> ( G e. USGraph <-> E : dom E -1-1-> { x e. ~P V | x ~~ 2o } ) )
Theorem	uspgrfen 16146*	The edge function of a simple pseudograph is a one-to-one function into unordered pairs of vertices. (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by AV, 13-Oct-2020.)
|- V = (Vtx ` G )   &    |- E = (iEdg ` G )   =>    |- ( G e. USPGraph -> E : dom E -1-1-> { x e. ~P V | ( x ~~ 1o \/ x ~~ 2o ) } )
Theorem	usgrfen 16147*	The edge function of a simple graph is a one-to-one function into the set of proper unordered pairs of vertices. (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by AV, 13-Oct-2020.)
|- V = (Vtx ` G )   &    |- E = (iEdg ` G )   =>    |- ( G e. USGraph -> E : dom E -1-1-> { x e. ~P V | x ~~ 2o } )
Theorem	usgrfun 16148	The edge function of a simple graph is a function. (Contributed by Alexander van der Vekens, 18-Aug-2017.) (Revised by AV, 13-Oct-2020.)
|- ( G e. USGraph -> Fun (iEdg ` G ) )
Theorem	usgredgssen 16149*	The set of edges of a simple graph is a subset of the set of proper unordered pairs of vertices. (Contributed by AV, 1-Jan-2020.) (Revised by AV, 14-Oct-2020.)
|- ( G e. USGraph -> (Edg ` G ) C_ { x e. ~P (Vtx ` G ) | x ~~ 2o } )
Theorem	edgusgren 16150	An edge of a simple graph is a proper unordered pair of vertices. (Contributed by AV, 1-Jan-2020.) (Revised by AV, 14-Oct-2020.)
|- ( ( G e. USGraph /\ E e. (Edg ` G ) ) -> ( E e. ~P (Vtx ` G ) /\ E ~~ 2o ) )
Theorem	isuspgropen 16151*	The property of being an undirected simple pseudograph represented as an ordered pair. The representation as an ordered pair is the usual representation of a graph, see section I.1 of [Bollobas] p. 1. (Contributed by AV, 25-Nov-2021.)
|- ( ( V e. W /\ E e. X ) -> ( <. V , E >. e. USPGraph <-> E : dom E -1-1-> { p e. ~P V | ( p ~~ 1o \/ p ~~ 2o ) } ) )
Theorem	isusgropen 16152*	The property of being an undirected simple graph represented as an ordered pair. The representation as an ordered pair is the usual representation of a graph, see section I.1 of [Bollobas] p. 1. (Contributed by AV, 30-Nov-2020.)
|- ( ( V e. W /\ E e. X ) -> ( <. V , E >. e. USGraph <-> E : dom E -1-1-> { p e. ~P V | p ~~ 2o } ) )
Theorem	usgrop 16153	A simple graph represented by an ordered pair. (Contributed by AV, 23-Oct-2020.) (Proof shortened by AV, 30-Nov-2020.)
|- ( G e. USGraph -> <. (Vtx ` G ) , (iEdg ` G ) >. e. USGraph )
Theorem	isausgren 16154*	The property of an ordered pair to be an alternatively defined simple graph, defined as a pair (V,E) of a set V (vertex set) and a set of unordered pairs of elements of V (edge set). (Contributed by Alexander van der Vekens, 28-Aug-2017.)
|- G = { <. v , e >. | e C_ { x e. ~P v | x ~~ 2o } }   =>    |- ( ( V e. W /\ E e. X ) -> ( V G E <-> E C_ { x e. ~P V | x ~~ 2o } ) )
Theorem	ausgrusgrben 16155*	The equivalence of the definitions of a simple graph. (Contributed by Alexander van der Vekens, 28-Aug-2017.) (Revised by AV, 14-Oct-2020.)
|- G = { <. v , e >. | e C_ { x e. ~P v | x ~~ 2o } }   =>    |- ( ( V e. X /\ E e. Y ) -> ( V G E <-> <. V , ( _I |` E ) >. e. USGraph ) )
Theorem	usgrausgrien 16156*	A simple graph represented by an alternatively defined simple graph. (Contributed by AV, 15-Oct-2020.)
|- G = { <. v , e >. | e C_ { x e. ~P v | x ~~ 2o } }   =>    |- ( H e. USGraph -> (Vtx ` H ) G (Edg ` H ) )
Theorem	ausgrumgrien 16157*	If an alternatively defined simple graph has the vertices and edges of an arbitrary graph, the arbitrary graph is an undirected multigraph. (Contributed by AV, 18-Oct-2020.) (Revised by AV, 25-Nov-2020.)
|- G = { <. v , e >. | e C_ { x e. ~P v | x ~~ 2o } }   =>    |- ( ( H e. W /\ (Vtx ` H ) G (Edg ` H ) /\ Fun (iEdg ` H ) ) -> H e. UMGraph )
Theorem	ausgrusgrien 16158*	The equivalence of the definitions of a simple graph, expressed with the set of vertices and the set of edges. (Contributed by AV, 15-Oct-2020.)
|- G = { <. v , e >. | e C_ { x e. ~P v | x ~~ 2o } }   &    |- O = { f | f : dom f -1-1-> ran f }   =>    |- ( ( H e. W /\ (Vtx ` H ) G (Edg ` H ) /\ (iEdg ` H ) e. O ) -> H e. USGraph )
Theorem	usgrausgrben 16159*	The equivalence of the definitions of a simple graph, expressed with the set of vertices and the set of edges. (Contributed by AV, 2-Jan-2020.) (Revised by AV, 15-Oct-2020.)
|- G = { <. v , e >. | e C_ { x e. ~P v | x ~~ 2o } }   &    |- O = { f | f : dom f -1-1-> ran f }   =>    |- ( ( H e. W /\ (iEdg ` H ) e. O ) -> ( (Vtx ` H ) G (Edg ` H ) <-> H e. USGraph ) )
Theorem	usgredgop 16160	An edge of a simple graph as second component of an ordered pair. (Contributed by Alexander van der Vekens, 17-Aug-2017.) (Proof shortened by Alexander van der Vekens, 16-Dec-2017.) (Revised by AV, 15-Oct-2020.)
|- ( ( G e. USGraph /\ E = (iEdg ` G ) /\ X e. dom E ) -> ( ( E ` X ) = { M , N } <-> <. X , { M , N } >. e. E ) )
Theorem	usgrf1o 16161	The edge function of a simple graph is a bijective function onto its range. (Contributed by Alexander van der Vekens, 18-Nov-2017.) (Revised by AV, 15-Oct-2020.)
|- E = (iEdg ` G )   =>    |- ( G e. USGraph -> E : dom E -1-1-onto-> ran E )
Theorem	usgrf1 16162	The edge function of a simple graph is a one to one function. (Contributed by Alexander van der Vekens, 18-Nov-2017.) (Revised by AV, 15-Oct-2020.)
|- E = (iEdg ` G )   =>    |- ( G e. USGraph -> E : dom E -1-1-> ran E )
Theorem	uspgrf1oedg 16163	The edge function of a simple pseudograph is a bijective function onto the edges of the graph. (Contributed by AV, 2-Jan-2020.) (Revised by AV, 15-Oct-2020.)
|- E = (iEdg ` G )   =>    |- ( G e. USPGraph -> E : dom E -1-1-onto-> (Edg ` G ) )
Theorem	usgrss 16164	An edge is a subset of vertices. (Contributed by Alexander van der Vekens, 19-Aug-2017.) (Revised by AV, 15-Oct-2020.)
|- E = (iEdg ` G )   &    |- V = (Vtx ` G )   =>    |- ( ( G e. USGraph /\ X e. dom E ) -> ( E ` X ) C_ V )
Theorem	uspgredgiedg 16165*	In a simple pseudograph, for each edge there is exactly one indexed edge. (Contributed by AV, 20-Apr-2025.)
|- E = (Edg ` G )   &    |- I = (iEdg ` G )   =>    |- ( ( G e. USPGraph /\ K e. E ) -> E! x e. dom I K = ( I ` x ) )
Theorem	uspgriedgedg 16166*	In a simple pseudograph, for each indexed edge there is exactly one edge. (Contributed by AV, 20-Apr-2025.)
|- E = (Edg ` G )   &    |- I = (iEdg ` G )   =>    |- ( ( G e. USPGraph /\ X e. dom I ) -> E! k e. E k = ( I ` X ) )
Theorem	uspgrushgr 16167	A simple pseudograph is an undirected simple hypergraph. (Contributed by AV, 19-Jan-2020.) (Revised by AV, 15-Oct-2020.)
|- ( G e. USPGraph -> G e. USHGraph )
Theorem	uspgrupgr 16168	A simple pseudograph is an undirected pseudograph. (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by AV, 15-Oct-2020.)
|- ( G e. USPGraph -> G e. UPGraph )
Theorem	uspgrupgrushgr 16169	A graph is a simple pseudograph iff it is a pseudograph and a simple hypergraph. (Contributed by AV, 30-Nov-2020.)
|- ( G e. USPGraph <-> ( G e. UPGraph /\ G e. USHGraph ) )
Theorem	usgruspgr 16170	A simple graph is a simple pseudograph. (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by AV, 15-Oct-2020.)
|- ( G e. USGraph -> G e. USPGraph )
Theorem	usgrumgr 16171	A simple graph is an undirected multigraph. (Contributed by AV, 25-Nov-2020.)
|- ( G e. USGraph -> G e. UMGraph )
Theorem	usgrumgruspgr 16172	A graph is a simple graph iff it is a multigraph and a simple pseudograph. (Contributed by AV, 30-Nov-2020.)
|- ( G e. USGraph <-> ( G e. UMGraph /\ G e. USPGraph ) )
Theorem	usgruspgrben 16173*	A class is a simple graph iff it is a simple pseudograph without loops. (Contributed by AV, 18-Oct-2020.)
|- ( G e. USGraph <-> ( G e. USPGraph /\ A. e e. (Edg ` G ) e ~~ 2o ) )
Theorem	uspgruhgr 16174	An undirected simple pseudograph is an undirected hypergraph. (Contributed by AV, 21-Apr-2025.)
|- ( G e. USPGraph -> G e. UHGraph )
Theorem	usgrupgr 16175	A simple graph is an undirected pseudograph. (Contributed by Alexander van der Vekens, 20-Aug-2017.) (Revised by AV, 15-Oct-2020.)
|- ( G e. USGraph -> G e. UPGraph )
Theorem	usgruhgr 16176	A simple graph is an undirected hypergraph. (Contributed by AV, 9-Feb-2018.) (Revised by AV, 15-Oct-2020.)
|- ( G e. USGraph -> G e. UHGraph )
Theorem	usgrislfuspgrdom 16177*	A simple graph is a loop-free simple pseudograph. (Contributed by AV, 27-Jan-2021.)
|- V = (Vtx ` G )   &    |- I = (iEdg ` G )   =>    |- ( G e. USGraph <-> ( G e. USPGraph /\ I : dom I --> { x e. ~P V | 2o ~<_ x } ) )
Theorem	uspgrun 16178	The union U of two simple pseudographs G and H with the same vertex set V is a pseudograph with the vertex V and the union ( E u. F ) of the (indexed) edges. (Contributed by AV, 16-Oct-2020.)
|- ( ph -> G e. USPGraph )   &    |- ( ph -> H e. USPGraph )   &    |- E = (iEdg ` G )   &    |- F = (iEdg ` H )   &    |- V = (Vtx ` G )   &    |- ( ph -> (Vtx ` H ) = V )   &    |- ( ph -> ( dom E i^i dom F ) = (/) )   &    |- ( ph -> U e. W )   &    |- ( ph -> (Vtx ` U ) = V )   &    |- ( ph -> (iEdg ` U ) = ( E u. F ) )   =>    |- ( ph -> U e. UPGraph )
Theorem	uspgrunop 16179	The union of two simple pseudographs (with the same vertex set): If <. V , E >. and <. V , F >. are simple pseudographs, then <. V , E u. F >. is a pseudograph (the vertex set stays the same, but the edges from both graphs are kept, maybe resulting in two edges between two vertices). (Contributed by Alexander van der Vekens, 10-Aug-2017.) (Revised by AV, 16-Oct-2020.) (Revised by AV, 24-Oct-2021.)
|- ( ph -> G e. USPGraph )   &    |- ( ph -> H e. USPGraph )   &    |- E = (iEdg ` G )   &    |- F = (iEdg ` H )   &    |- V = (Vtx ` G )   &    |- ( ph -> (Vtx ` H ) = V )   &    |- ( ph -> ( dom E i^i dom F ) = (/) )   =>    |- ( ph -> <. V , ( E u. F ) >. e. UPGraph )
Theorem	usgrun 16180	The union U of two simple graphs G and H with the same vertex set V is a multigraph (not necessarily a simple graph!) with the vertex V and the union ( E u. F ) of the (indexed) edges. (Contributed by AV, 29-Nov-2020.)
|- ( ph -> G e. USGraph )   &    |- ( ph -> H e. USGraph )   &    |- E = (iEdg ` G )   &    |- F = (iEdg ` H )   &    |- V = (Vtx ` G )   &    |- ( ph -> (Vtx ` H ) = V )   &    |- ( ph -> ( dom E i^i dom F ) = (/) )   &    |- ( ph -> U e. W )   &    |- ( ph -> (Vtx ` U ) = V )   &    |- ( ph -> (iEdg ` U ) = ( E u. F ) )   =>    |- ( ph -> U e. UMGraph )
Theorem	usgrunop 16181	The union of two simple graphs (with the same vertex set): If <. V , E >. and <. V , F >. are simple graphs, then <. V , E u. F >. is a multigraph (not necessarily a simple graph!) - the vertex set stays the same, but the edges from both graphs are kept, possibly resulting in two edges between two vertices. (Contributed by AV, 29-Nov-2020.)
|- ( ph -> G e. USGraph )   &    |- ( ph -> H e. USGraph )   &    |- E = (iEdg ` G )   &    |- F = (iEdg ` H )   &    |- V = (Vtx ` G )   &    |- ( ph -> (Vtx ` H ) = V )   &    |- ( ph -> ( dom E i^i dom F ) = (/) )   =>    |- ( ph -> <. V , ( E u. F ) >. e. UMGraph )
Theorem	usgredg2en 16182	The value of the "edge function" of a simple graph is a set containing two elements (the vertices the corresponding edge is connecting). (Contributed by Alexander van der Vekens, 11-Aug-2017.) (Revised by AV, 16-Oct-2020.) (Proof shortened by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   =>    |- ( ( G e. USGraph /\ X e. dom E ) -> ( E ` X ) ~~ 2o )
Theorem	usgredgprv 16183	In a simple graph, an edge is an unordered pair of vertices. (Contributed by Alexander van der Vekens, 19-Aug-2017.) (Revised by AV, 16-Oct-2020.) (Proof shortened by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   &    |- V = (Vtx ` G )   =>    |- ( ( G e. USGraph /\ X e. dom E ) -> ( ( E ` X ) = { M , N } -> ( M e. V /\ N e. V ) ) )
Theorem	usgredgppren 16184	An edge of a simple graph is a proper pair, i.e. a set containing two different elements (the endvertices of the edge). Analogue of usgredg2en 16182. (Contributed by Alexander van der Vekens, 11-Aug-2017.) (Revised by AV, 9-Jan-2020.) (Revised by AV, 23-Oct-2020.)
|- E = (Edg ` G )   =>    |- ( ( G e. USGraph /\ C e. E ) -> C ~~ 2o )
Theorem	usgrpredgv 16185	An edge of a simple graph always connects two vertices. Analogue of usgredgprv 16183. (Contributed by Alexander van der Vekens, 7-Oct-2017.) (Revised by AV, 9-Jan-2020.) (Revised by AV, 23-Oct-2020.) (Proof shortened by AV, 27-Nov-2020.)
|- E = (Edg ` G )   &    |- V = (Vtx ` G )   =>    |- ( ( G e. USGraph /\ { M , N } e. E ) -> ( M e. V /\ N e. V ) )
Theorem	edgssv2en 16186	An edge of a simple graph is a proper unordered pair of vertices, i.e. a subset of the set of vertices of size 2. (Contributed by AV, 10-Jan-2020.) (Revised by AV, 23-Oct-2020.)
|- V = (Vtx ` G )   &    |- E = (Edg ` G )   =>    |- ( ( G e. USGraph /\ C e. E ) -> ( C C_ V /\ C ~~ 2o ) )
Theorem	usgredg 16187*	For each edge in a simple graph, there are two distinct vertices which are connected by this edge. (Contributed by Alexander van der Vekens, 9-Dec-2017.) (Revised by AV, 17-Oct-2020.) (Shortened by AV, 25-Nov-2020.)
|- V = (Vtx ` G )   &    |- E = (Edg ` G )   =>    |- ( ( G e. USGraph /\ C e. E ) -> E. a e. V E. b e. V ( a =/= b /\ C = { a , b } ) )
Theorem	usgrnloopv 16188	In a simple graph, there is no loop, i.e. no edge connecting a vertex with itself. (Contributed by Alexander van der Vekens, 26-Jan-2018.) (Revised by AV, 17-Oct-2020.) (Proof shortened by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   =>    |- ( ( G e. USGraph /\ M e. W ) -> ( ( E ` X ) = { M , N } -> M =/= N ) )
Theorem	usgrnloop 16189*	In a simple graph, there is no loop, i.e. no edge connecting a vertex with itself. (Contributed by Alexander van der Vekens, 19-Aug-2017.) (Proof shortened by Alexander van der Vekens, 20-Mar-2018.) (Revised by AV, 17-Oct-2020.) (Proof shortened by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   =>    |- ( G e. USGraph -> ( E. x e. dom E ( E ` x ) = { M , N } -> M =/= N ) )
Theorem	usgrnloop0 16190*	A simple graph has no loops. (Contributed by Alexander van der Vekens, 6-Dec-2017.) (Revised by AV, 17-Oct-2020.) (Proof shortened by AV, 11-Dec-2020.)
|- E = (iEdg ` G )   =>    |- ( G e. USGraph -> { x e. dom E | ( E ` x ) = { U } } = (/) )
Theorem	usgredgne 16191	An edge of a simple graph always connects two different vertices. Analogue of usgrnloopv 16188 resp. usgrnloop 16189. (Contributed by Alexander van der Vekens, 2-Sep-2017.) (Revised by AV, 17-Oct-2020.) (Proof shortened by AV, 27-Nov-2020.)
|- E = (Edg ` G )   =>    |- ( ( G e. USGraph /\ { M , N } e. E ) -> M =/= N )
Theorem	usgrf1oedg 16192	The edge function of a simple graph is a 1-1 function onto the set of edges. (Contributed by AV, 18-Oct-2020.)
|- I = (iEdg ` G )   &    |- E = (Edg ` G )   =>    |- ( G e. USGraph -> I : dom I -1-1-onto-> E )
Theorem	uhgr2edg 16193*	If a vertex is adjacent to two different vertices in a hypergraph, there are more than one edges starting at this vertex. (Contributed by Alexander van der Vekens, 10-Dec-2017.) (Revised by AV, 11-Feb-2021.)
|- I = (iEdg ` G )   &    |- E = (Edg ` G )   &    |- V = (Vtx ` G )   =>    |- ( ( ( G e. UHGraph /\ A =/= B ) /\ ( A e. V /\ B e. V /\ N e. V ) /\ ( { N , A } e. E /\ { B , N } e. E ) ) -> E. x e. dom I E. y e. dom I ( x =/= y /\ N e. ( I ` x ) /\ N e. ( I ` y ) ) )
Theorem	umgr2edg 16194*	If a vertex is adjacent to two different vertices in a multigraph, there are more than one edges starting at this vertex. (Contributed by Alexander van der Vekens, 10-Dec-2017.) (Revised by AV, 11-Feb-2021.)
|- I = (iEdg ` G )   &    |- E = (Edg ` G )   =>    |- ( ( ( G e. UMGraph /\ A =/= B ) /\ ( { N , A } e. E /\ { B , N } e. E ) ) -> E. x e. dom I E. y e. dom I ( x =/= y /\ N e. ( I ` x ) /\ N e. ( I ` y ) ) )
Theorem	usgr2edg 16195*	If a vertex is adjacent to two different vertices in a simple graph, there are more than one edges starting at this vertex. (Contributed by Alexander van der Vekens, 10-Dec-2017.) (Revised by AV, 17-Oct-2020.) (Proof shortened by AV, 11-Feb-2021.)
|- I = (iEdg ` G )   &    |- E = (Edg ` G )   =>    |- ( ( ( G e. USGraph /\ A =/= B ) /\ ( { N , A } e. E /\ { B , N } e. E ) ) -> E. x e. dom I E. y e. dom I ( x =/= y /\ N e. ( I ` x ) /\ N e. ( I ` y ) ) )
Theorem	umgr2edg1 16196*	If a vertex is adjacent to two different vertices in a multigraph, there is not only one edge starting at this vertex. (Contributed by Alexander van der Vekens, 10-Dec-2017.) (Revised by AV, 8-Jun-2021.)
|- I = (iEdg ` G )   &    |- E = (Edg ` G )   =>    |- ( ( ( G e. UMGraph /\ A =/= B ) /\ ( { N , A } e. E /\ { B , N } e. E ) ) -> -. E! x e. dom I N e. ( I ` x ) )
Theorem	usgr2edg1 16197*	If a vertex is adjacent to two different vertices in a simple graph, there is not only one edge starting at this vertex. (Contributed by Alexander van der Vekens, 10-Dec-2017.) (Revised by AV, 17-Oct-2020.) (Proof shortened by AV, 8-Jun-2021.)
|- I = (iEdg ` G )   &    |- E = (Edg ` G )   =>    |- ( ( ( G e. USGraph /\ A =/= B ) /\ ( { N , A } e. E /\ { B , N } e. E ) ) -> -. E! x e. dom I N e. ( I ` x ) )
Theorem	umgrvad2edg 16198*	If a vertex is adjacent to two different vertices in a multigraph, there are more than one edges starting at this vertex, analogous to usgr2edg 16195. (Contributed by Alexander van der Vekens, 10-Dec-2017.) (Revised by AV, 9-Jan-2020.) (Revised by AV, 8-Jun-2021.)
|- E = (Edg ` G )   =>    |- ( ( ( G e. UMGraph /\ A =/= B ) /\ ( { N , A } e. E /\ { B , N } e. E ) ) -> E. x e. E E. y e. E ( x =/= y /\ N e. x /\ N e. y ) )
Theorem	umgr2edgneu 16199*	If a vertex is adjacent to two different vertices in a multigraph, there is not only one edge starting at this vertex, analogous to usgr2edg1 16197. Lemma for theorems about friendship graphs. (Contributed by Alexander van der Vekens, 10-Dec-2017.) (Revised by AV, 9-Jan-2020.)
|- E = (Edg ` G )   =>    |- ( ( ( G e. UMGraph /\ A =/= B ) /\ ( { N , A } e. E /\ { B , N } e. E ) ) -> -. E! x e. E N e. x )
Theorem	usgrsizedgen 16200	In a simple graph, the size of the edge function is the number of the edges of the graph. (Contributed by AV, 4-Jan-2020.) (Revised by AV, 7-Jun-2021.)
|- ( G e. USGraph -> (iEdg ` G ) ~~ (Edg ` G ) )