let G1, G2 be _Graph; for F being continuous PGraphMapping of G1,G2 st rng (F _V) = the_Vertices_of G2 & G1 is loopless holds
G2 is loopless
let F be continuous PGraphMapping of G1,G2; ( rng (F _V) = the_Vertices_of G2 & G1 is loopless implies G2 is loopless )
assume A1:
rng (F _V) = the_Vertices_of G2
; ( not G1 is loopless or G2 is loopless )
assume A2:
G1 is loopless
; G2 is loopless
for v, e being object holds not e Joins v,v,G2
proof
let v be
object ;
for e being object holds not e Joins v,v,G2
given e9 being
object such that A3:
e9 Joins v,
v,
G2
;
contradiction
v in rng (F _V)
by A1, A3, GLIB_000:13;
then consider v0 being
object such that A4:
(
v0 in dom (F _V) &
(F _V) . v0 = v )
by FUNCT_1:def 3;
consider e being
object such that A5:
(
e Joins v0,
v0,
G1 &
e in dom (F _E) &
(F _E) . e = e9 )
by A3, A4, Def16;
thus
contradiction
by A2, A5, GLIB_000:18;
verum
end;
hence
G2 is loopless
by GLIB_000:18; verum