Theorem eqeq12 2245

Description: Equality relationship among 4 classes. (Contributed by NM, 3-Aug-1994.)

Assertion

Ref	Expression
eqeq12	|- ( ( A = B /\ C = D ) -> ( A = C <-> B = D ) )

Proof of Theorem eqeq12

Step	Hyp	Ref	Expression
1		eqeq1 2239	. 2 |- ( A = B -> ( A = C <-> B = C ) )
2		eqeq2 2242	. 2 |- ( C = D -> ( B = C <-> B = D ) )
3	1, 2	sylan9bb 462	1 |- ( ( A = B /\ C = D ) -> ( A = C <-> B = D ) )

Syntax hints:   -> wi 4   /\ wa 104   <-> wb 105   = wceq 1398

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-5 1496  ax-gen 1498  ax-4 1559  ax-17 1575  ax-ext 2214

This theorem depends on definitions:  df-bi 117  df-cleq 2225

This theorem is referenced by:  eqeq12i  2246  eqeq12d  2247  eqeqan12d  2248  funopg  5386  riotaeqimp  6028  fvdifsuppst  6444  tfri3  6598  th3qlem1  6871  xpdom2  7082  difinfsnlem  7390  difinfsn  7391  xrlttri3  10130  bcn1  11120  summodc  12069  prodmodc  12264  ringinvnz1ne0  14193  wlkres  16374