Theorem eqeqan12d 2254

Description: A useful inference for substituting definitions into an equality. (Contributed by NM, 9-Aug-1994.) (Proof shortened by Andrew Salmon, 25-May-2011.)

Hypotheses

Ref	Expression
eqeqan12d.1	|- ( ph -> A = B )
eqeqan12d.2	|- ( ps -> C = D )

Assertion

Ref	Expression
eqeqan12d	|- ( ( ph /\ ps ) -> ( A = C <-> B = D ) )

Proof of Theorem eqeqan12d

Step	Hyp	Ref	Expression
1		eqeqan12d.1	. 2 |- ( ph -> A = B )
2		eqeqan12d.2	. 2 |- ( ps -> C = D )
3		eqeq12 2251	. 2 |- ( ( A = B /\ C = D ) -> ( A = C <-> B = D ) )
4	1, 2, 3	syl2an 289	1 |- ( ( ph /\ ps ) -> ( A = C <-> B = D ) )

This proof depends on syntax axioms:   -> wi 4   /\ wa 104   <-> wb 105   = wceq 1402

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-5 1500  ax-gen 1502  ax-4 1563  ax-17 1579  ax-ext 2220

This proof depends on definitions:  df-bi 117  df-cleq 2231

This theorem is used by:  eqeqan12rd  2255  eqfnfv  5809  eqfnfv2  5810  f1mpt  5980  xpopth  6414  f1o2ndf1  6468  ecopoveq  6908  xpdom2  7133  djune  7424  addpipqqs  7743  enq0enq  7804  enq0sym  7805  enq0tr  7807  enq0breq  7809  preqlu  7845  cnegexlem1  8508  neg11  8584  subeqrev  8709  cnref1o  10068  xneg11  10253  modlteq  10855  sq11  11070  qsqeqor  11108  fz1eqb  11251  eqwrd  11367  s111  11421  ccatopth  11510  wrd2ind  11517  cj11  11693  sqrt11  11827  sqabs  11871  recan  11898  reeff1  12492  efieq  12527  xpsff1o  13729  ismhm  13827  isdomn  14687  tgtop11  15302  ioocosf1o  16082  mpodvdsmulf1o  16284  iswlk  16769