let G1, G2 be Graph; :: thesis: ( ex G being Graph st
( G1 c= G & G2 c= G ) implies ( G1 c= G1 \/ G2 & G2 c= G1 \/ G2 ) )
given G being Graph such that A1: ( G1 c= G & G2 c= G ) ; :: thesis: ( G1 c= G1 \/ G2 & G2 c= G1 \/ G2 )
A2: ( the Source of G1 c= the Source of G & the Source of G2 c= the Source of G ) by A1, Th5;
A3: ( the Target of G1 c= the Target of G & the Target of G2 c= the Target of G ) by A1, Th5;
A4: the Source of G1 tolerates the Source of G2 by A2, PARTFUN1:57;
the Target of G1 tolerates the Target of G2 by A3, PARTFUN1:57;
hence ( G1 c= G1 \/ G2 & G2 c= G1 \/ G2 ) by A4, Th19; :: thesis: verum