Theorem ssiun2 3909

Description: Identity law for subset of an indexed union. (Contributed by NM, 12-Oct-2003.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)

Assertion

Ref	Expression
ssiun2	|- ( x e. A -> B C_ U_ x e. A B )

Proof of Theorem ssiun2

Dummy variable y is distinct from all other variables.

Step	Hyp	Ref	Expression
1		rspe 2515	. . . 4 |- ( ( x e. A /\ y e. B ) -> E. x e. A y e. B )
2	1	ex 114	. . 3 |- ( x e. A -> ( y e. B -> E. x e. A y e. B ) )
3		eliun 3870	. . 3 |- ( y e. U_ x e. A B <-> E. x e. A y e. B )
4	2, 3	syl6ibr 161	. 2 |- ( x e. A -> ( y e. B -> y e. U_ x e. A B ) )
5	4	ssrdv 3148	1 |- ( x e. A -> B C_ U_ x e. A B )

Syntax hints:   -> wi 4   e. wcel 2136   E.wrex 2445   C_ wss 3116   U_ciun 3866

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-io 699  ax-5 1435  ax-7 1436  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-8 1492  ax-10 1493  ax-11 1494  ax-i12 1495  ax-bndl 1497  ax-4 1498  ax-17 1514  ax-i9 1518  ax-ial 1522  ax-i5r 1523  ax-ext 2147

This theorem depends on definitions:  df-bi 116  df-tru 1346  df-nf 1449  df-sb 1751  df-clab 2152  df-cleq 2158  df-clel 2161  df-nfc 2297  df-ral 2449  df-rex 2450  df-v 2728  df-in 3122  df-ss 3129  df-iun 3868

This theorem is referenced by:  ssiun2s  3910  triun  4093  ixpf  6686