Metamath Proof Explorer

Theorem coex

Description: The composition of two sets is a set. (Contributed by NM, 15-Dec-2003)

Ref Expression
Hypotheses coex.1 A V
coex.2 B V
Assertion coex A B V


Step Hyp Ref Expression
1 coex.1 A V
2 coex.2 B V
3 coexg A V B V A B V
4 1 2 3 mp2an A B V