Theorem ifssun 3641

Description: A conditional class is included in the union of its two alternatives. (Contributed by BJ, 15-Aug-2024.)

Assertion

Ref	Expression
ifssun	|- if ( ph , A , B ) C_ ( A u. B )

Proof of Theorem ifssun

Dummy variable x is distinct from all other variables.

Step	Hyp	Ref	Expression
1		dfif6 3626	. 2 |- if ( ph , A , B ) = ( { x e. A | ph } u. { x e. B | -. ph } )
2		ssrab2 3327	. . 3 |- { x e. A | ph } C_ A
3		ssrab2 3327	. . 3 |- { x e. B | -. ph } C_ B
4		unss12 3395	. . 3 |- ( ( { x e. A | ph } C_ A /\ { x e. B | -. ph } C_ B ) -> ( { x e. A | ph } u. { x e. B | -. ph } ) C_ ( A u. B ) )
5	2, 3, 4	mp2an 426	. 2 |- ( { x e. A | ph } u. { x e. B | -. ph } ) C_ ( A u. B )
6	1, 5	eqsstri 3274	1 |- if ( ph , A , B ) C_ ( A u. B )

Syntax hints:   -. wn 3   {crab 2526   u. cun 3212   C_ wss 3214   ifcif 3624

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 717  ax-5 1496  ax-7 1497  ax-gen 1498  ax-ie1 1542  ax-ie2 1543  ax-8 1553  ax-10 1554  ax-11 1555  ax-i12 1556  ax-bndl 1558  ax-4 1559  ax-17 1575  ax-i9 1579  ax-ial 1583  ax-i5r 1584  ax-ext 2216

This theorem depends on definitions:  df-bi 117  df-tru 1401  df-nf 1510  df-sb 1812  df-clab 2221  df-cleq 2227  df-clel 2230  df-nfc 2375  df-rab 2531  df-v 2817  df-un 3218  df-in 3220  df-ss 3227  df-if 3625

This theorem is referenced by:  ifidss  3642  ifelpwung  4607