Theorem eqeq12 2244

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 2238	. 2 |- ( A = B -> ( A = C <-> B = C ) )
2		eqeq2 2241	. 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 2213

This theorem depends on definitions:  df-bi 117  df-cleq 2224

This theorem is referenced by:  eqeq12i  2245  eqeq12d  2246  eqeqan12d  2247  funopg  5367  riotaeqimp  6006  fvdifsuppst  6422  tfri3  6576  th3qlem1  6849  xpdom2  7058  difinfsnlem  7358  difinfsn  7359  xrlttri3  10093  bcn1  11083  summodc  12024  prodmodc  12219  ringinvnz1ne0  14143  wlkres  16320