let G, G1, G2 be Graph; :: thesis: ( G1 c= G & G2 c= G implies G1 \/ G2 c= G )
assume A1: ( G1 c= G & G2 c= G ) ; :: thesis: G1 \/ G2 c= G
then A2: ( the Source of G1 c= the Source of G & the Source of G2 c= the Source of G ) by 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;
then G1 \/ G2 is_sum_of G1,G2 by A4;
hence G1 \/ G2 c= G by A1, Th21; :: thesis: verum