let c be Cardinal; :: thesis: for G1, G2 being _Graph st G1 == G2 & G1 is c -regular holds
G2 is c -regular
let G1, G2 be _Graph; :: thesis: ( G1 == G2 & G1 is c -regular implies G2 is c -regular )
assume G1 == G2 ; :: thesis: ( not G1 is c -regular or G2 is c -regular )
then consider F being PGraphMapping of G1,G2 such that
A1: ( F = id G1 & F is Disomorphism ) by GLIBPRE0:75;
thus ( not G1 is c -regular or G2 is c -regular ) by A1, Lm2; :: thesis: verum