Theorem ifnefalse 3569

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 3566 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 2365	. 2 |- ( A =/= B <-> -. A = B )
2		iffalse 3566	. 2 |- ( -. A = B -> if ( A = B , C , D ) = D )
3	1, 2	sylbi 121	1 |- ( A =/= B -> if ( A = B , C , D ) = D )

Syntax hints:   -. wn 3   -> wi 4   = wceq 1364   =/= wne 2364   ifcif 3558

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-in2 616  ax-io 710  ax-5 1458  ax-7 1459  ax-gen 1460  ax-ie1 1504  ax-ie2 1505  ax-8 1515  ax-11 1517  ax-4 1521  ax-17 1537  ax-i9 1541  ax-ial 1545  ax-i5r 1546  ax-ext 2175

This theorem depends on definitions:  df-bi 117  df-nf 1472  df-sb 1774  df-clab 2180  df-cleq 2186  df-clel 2189  df-ne 2365  df-if 3559

This theorem is referenced by:  xnegmnf  9898  rexneg  9899  xaddpnf1  9915  xaddpnf2  9916  xaddmnf1  9917  xaddmnf2  9918  mnfaddpnf  9920  rexadd  9921  fztpval  10152  pcval  12437  xpsfrnel  12930  znf1o  14150  znfi  14154  znhash  14155  lgsval3  15175  lgsdinn0  15205