Theorem eqeq12 2247

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 2241	. 2 |- ( A = B -> ( A = C <-> B = C ) )
2		eqeq2 2244	. 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 2216

This theorem depends on definitions:  df-bi 117  df-cleq 2227

This theorem is referenced by:  eqeq12i  2248  eqeq12d  2249  eqeqan12d  2250  funopg  5391  riotaeqimp  6036  fvdifsuppst  6457  tfri3  6611  th3qlem1  6884  xpdom2  7095  difinfsnlem  7403  difinfsn  7404  xrlttri3  10149  bcn1  11145  summodc  12094  prodmodc  12289  ringinvnz1ne0  14292  wlkres  16500