Metamath Proof Explorer

Theorem dfiun2

Description: Alternate definition of indexed union when B is a set. Definition 15(a) of Suppes p. 44. (Contributed by NM, 27-Jun-1998) (Revised by David Abernethy, 19-Jun-2012)

Ref Expression
Hypothesis dfiun2.1 B V
Assertion dfiun2 x A B = y | x A y = B


Step Hyp Ref Expression
1 dfiun2.1 B V
2 dfiun2g x A B V x A B = y | x A y = B
3 1 a1i x A B V
4 2 3 mprg x A B = y | x A y = B