Theorem eqeq12 2251

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 2245	. 2 |- ( A = B -> ( A = C <-> B = C ) )
2		eqeq2 2248	. 2 |- ( C = D -> ( B = C <-> B = D ) )
3	1, 2	sylan9bb 466	1 |- ( ( A = B /\ C = D ) -> ( A = C <-> B = D ) )

Syntax hints:   -> wi 4   /\ wa 104   <-> wb 105   = wceq 1402

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 1500  ax-gen 1502  ax-4 1563  ax-17 1579  ax-ext 2220

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

This theorem is referenced by:  eqeq12i  2252  eqeq12d  2253  eqeqan12d  2254  funopg  5406  riotaeqimp  6053  fvdifsuppst  6474  tfri3  6628  th3qlem1  6901  xpdom2  7119  difinfsnlem  7429  difinfsn  7430  xrlttri3  10178  bcn1  11174  summodc  12128  prodmodc  12323  ringinvnz1ne0  14327  wlkres  16534