Theorem ifnefalse 3537

Description: When values are unequal, but an "if" condition checks if they are equal, then the "false" branch results. This is a simple utility to provide a slight shortening and simplification of proofs versus applying iffalse 3534 directly in this case. (Contributed by David A. Wheeler, 15-May-2015.)

Assertion

Ref	Expression
ifnefalse	|- ( A =/= B -> if ( A = B , C , D ) = D )

Proof of Theorem ifnefalse

Step	Hyp	Ref	Expression
1		df-ne 2341	. 2 |- ( A =/= B <-> -. A = B )
2		iffalse 3534	. 2 |- ( -. A = B -> if ( A = B , C , D ) = D )
3	1, 2	sylbi 120	1 |- ( A =/= B -> if ( A = B , C , D ) = D )

Syntax hints:   -. wn 3   -> wi 4   = wceq 1348   =/= wne 2340   ifcif 3526

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-in2 610  ax-io 704  ax-5 1440  ax-7 1441  ax-gen 1442  ax-ie1 1486  ax-ie2 1487  ax-8 1497  ax-11 1499  ax-4 1503  ax-17 1519  ax-i9 1523  ax-ial 1527  ax-i5r 1528  ax-ext 2152

This theorem depends on definitions:  df-bi 116  df-nf 1454  df-sb 1756  df-clab 2157  df-cleq 2163  df-clel 2166  df-ne 2341  df-if 3527

This theorem is referenced by:  xnegmnf  9786  rexneg  9787  xaddpnf1  9803  xaddpnf2  9804  xaddmnf1  9805  xaddmnf2  9806  mnfaddpnf  9808  rexadd  9809  fztpval  10039  pcval  12250  lgsval3  13713  lgsdinn0  13743