Definition df-clwlks 26667

Description: Define the set of all closed walks (in an undirected graph).

According to definition 4 in [Huneke] p. 2: "A walk of length n on (a graph) G is an ordered sequence v0 , v1 , ... v(n) of vertices such that v(i) and v(i+1) are neighbors (i.e are connected by an edge). We say the walk is closed if v(n) = v0".

According to the definition of a walk as two mappings f from { 0 , ... , ( n - 1 ) } and p from { 0 , ... , n }, where f enumerates the (indices of the) edges, and p enumerates the vertices, a closed walk is represented by the following sequence: p(0) e(f(0)) p(1) e(f(1)) ... p(n-1) e(f(n-1)) p(n)=p(0).

Notice that by this definition, a single vertex is a closed walk of length 0, see also 0clwlk 26991! (Contributed by Alexander van der Vekens, 12-Mar-2018.) (Revised by AV, 16-Feb-2021.)

Assertion

Ref	Expression
df-clwlks	|- ClWalks = ( g e. _V |-> { <. f , p >. | ( f (Walks ` g ) p /\ ( p ` 0 ) = ( p ` ( # ` f ) ) ) } )

Distinct variable group:   f, g, p

Detailed syntax breakdown of Definition df-clwlks

Step	Hyp	Ref	Expression
1		cclwlks 26666	. 2 class ClWalks
2		vg	. . 3 setvar g
3		cvv 3200	. . 3 class _V
4		vf	. . . . . . 7 setvar f
5	4	cv 1482	. . . . . 6 class f
6		vp	. . . . . . 7 setvar p
7	6	cv 1482	. . . . . 6 class p
8	2	cv 1482	. . . . . . 7 class g
9		cwlks 26492	. . . . . . 7 class Walks
10	8, 9	cfv 5888	. . . . . 6 class (Walks ` g )
11	5, 7, 10	wbr 4653	. . . . 5 wff f (Walks ` g ) p
12		cc0 9936	. . . . . . 7 class 0
13	12, 7	cfv 5888	. . . . . 6 class ( p ` 0 )
14		chash 13117	. . . . . . . 8 class #
15	5, 14	cfv 5888	. . . . . . 7 class ( # ` f )
16	15, 7	cfv 5888	. . . . . 6 class ( p ` ( # ` f ) )
17	13, 16	wceq 1483	. . . . 5 wff ( p ` 0 ) = ( p ` ( # ` f ) )
18	11, 17	wa 384	. . . 4 wff ( f (Walks ` g ) p /\ ( p ` 0 ) = ( p ` ( # ` f ) ) )
19	18, 4, 6	copab 4712	. . 3 class { <. f , p >. | ( f (Walks ` g ) p /\ ( p ` 0 ) = ( p ` ( # ` f ) ) ) }
20	2, 3, 19	cmpt 4729	. 2 class ( g e. _V |-> { <. f , p >. | ( f (Walks ` g ) p /\ ( p ` 0 ) = ( p ` ( # ` f ) ) ) } )
21	1, 20	wceq 1483	1 wff ClWalks = ( g e. _V |-> { <. f , p >. | ( f (Walks ` g ) p /\ ( p ` 0 ) = ( p ` ( # ` f ) ) ) } )

This definition is referenced by:  clwlks  26668