Theorem ifidss 3520

Description: A conditional class whose two alternatives are equal is included in that alternative. With excluded middle, we can prove it is equal to it. (Contributed by BJ, 15-Aug-2024.)

Assertion

Ref	Expression
ifidss	|- if ( ph , A , A ) C_ A

Proof of Theorem ifidss

Step	Hyp	Ref	Expression
1		ifssun 3519	. 2 |- if ( ph , A , A ) C_ ( A u. A )
2		unidm 3250	. 2 |- ( A u. A ) = A
3	1, 2	sseqtri 3162	1 |- if ( ph , A , A ) C_ A

Syntax hints:   u. cun 3100   C_ wss 3102   ifcif 3505

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 1427  ax-7 1428  ax-gen 1429  ax-ie1 1473  ax-ie2 1474  ax-8 1484  ax-10 1485  ax-11 1486  ax-i12 1487  ax-bndl 1489  ax-4 1490  ax-17 1506  ax-i9 1510  ax-ial 1514  ax-i5r 1515  ax-ext 2139

This theorem depends on definitions:  df-bi 116  df-tru 1338  df-nf 1441  df-sb 1743  df-clab 2144  df-cleq 2150  df-clel 2153  df-nfc 2288  df-rab 2444  df-v 2714  df-un 3106  df-in 3108  df-ss 3115  df-if 3506

This theorem is referenced by: (None)