let G be Graph; :: thesis: (rng the Source of G) \/ (rng the Target of G) c= the carrier of G
( rng the Source of G c= the carrier of G & rng the Target of G c= the carrier of G ) by RELAT_1:def 19;
hence (rng the Source of G) \/ (rng the Target of G) c= the carrier of G by XBOOLE_1:8; :: thesis: verum