let G be _Graph; ( G is _trivial & G is Cycle-like implies ( G is non-multi & G is loopfull ) )
assume A6:
( G is _trivial & G is Cycle-like )
; ( G is non-multi & G is loopfull )
then 1 =
G .order()
by GLIB_000:26
.=
G .size()
by A6, Th40
;
then consider e being object such that
A7:
the_Edges_of G = {e}
by CARD_2:42;
now for e1, e2, v1, v2 being object st e1 Joins v1,v2,G & e2 Joins v1,v2,G holds
e1 = e2let e1,
e2,
v1,
v2 be
object ;
( e1 Joins v1,v2,G & e2 Joins v1,v2,G implies e1 = e2 )assume
(
e1 Joins v1,
v2,
G &
e2 Joins v1,
v2,
G )
;
e1 = e2then
(
e1 in the_Edges_of G &
e2 in the_Edges_of G )
by GLIB_000:def 13;
hence
e1 = e2
by A7, ZFMISC_1:def 10;
verum end;
hence
G is non-multi
by GLIB_000:def 20; G is loopfull
now for v being Vertex of G ex e being object st e Joins v,v,Glet v be
Vertex of
G;
ex e being object st e Joins v,v,Gtake e =
e;
e Joins v,v,Gset u =
(the_Source_of G) . e;
set w =
(the_Target_of G) . e;
e in the_Edges_of G
by A7, TARSKI:def 1;
then A8:
e Joins (the_Source_of G) . e,
(the_Target_of G) . e,
G
by GLIB_000:def 13;
then reconsider u =
(the_Source_of G) . e,
w =
(the_Target_of G) . e as
Vertex of
G by GLIB_000:13;
(
v = u &
v = w )
by A6, ZFMISC_1:def 10;
hence
e Joins v,
v,
G
by A8;
verum end;
hence
G is loopfull
by GLIB_012:def 1; verum