Definition df-trls 16100

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

According to Wikipedia ("Path (graph theory)", https://en.wikipedia.org/wiki/Path_(graph_theory), 3-Oct-2017): "A trail is a walk in which all edges are distinct.

According to Bollobas: "... walk is called a trail if all its edges are distinct.", see Definition of [Bollobas] p. 5.

Therefore, a trail can be represented by an injective mapping f from { 1 , ... , n } and a mapping p from { 0 , ... , n }, where f enumerates the (indices of the) different edges, and p enumerates the vertices. So the trail is also represented by the following sequence: p(0) e(f(1)) p(1) e(f(2)) ... p(n-1) e(f(n)) p(n). (Contributed by Alexander van der Vekens and Mario Carneiro, 4-Oct-2017.) (Revised by AV, 28-Dec-2020.)

Assertion

Ref	Expression
df-trls	|- Trails = ( g e. _V |-> { <. f , p >. | ( f (Walks ` g ) p /\ Fun `' f ) } )

Distinct variable group:   f, g, p

Detailed syntax breakdown of Definition df-trls

Step	Hyp	Ref	Expression
1		ctrls 16099	. 2 class Trails
2		vg	. . 3 setvar g
3		cvv 2799	. . 3 class _V
4		vf	. . . . . . 7 setvar f
5	4	cv 1394	. . . . . 6 class f
6		vp	. . . . . . 7 setvar p
7	6	cv 1394	. . . . . 6 class p
8	2	cv 1394	. . . . . . 7 class g
9		cwlks 16038	. . . . . . 7 class Walks
10	8, 9	cfv 5318	. . . . . 6 class (Walks ` g )
11	5, 7, 10	wbr 4083	. . . . 5 wff f (Walks ` g ) p
12	5	ccnv 4718	. . . . . 6 class `' f
13	12	wfun 5312	. . . . 5 wff Fun `' f
14	11, 13	wa 104	. . . 4 wff ( f (Walks ` g ) p /\ Fun `' f )
15	14, 4, 6	copab 4144	. . 3 class { <. f , p >. | ( f (Walks ` g ) p /\ Fun `' f ) }
16	2, 3, 15	cmpt 4145	. 2 class ( g e. _V |-> { <. f , p >. | ( f (Walks ` g ) p /\ Fun `' f ) } )
17	1, 16	wceq 1395	1 wff Trails = ( g e. _V |-> { <. f , p >. | ( f (Walks ` g ) p /\ Fun `' f ) } )

This definition is referenced by:  reltrls  16101  trlsfvalg  16102  trlsv  16103