Theorem eqeq12 2365

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 2359	. 2 |- (A = B -> (A = C <-> B = C))
2		eqeq2 2362	. 2 |- (C = D -> (B = C <-> B = D))
3	1, 2	sylan9bb 680	1 |- ((A = B /\ C = D) -> (A = C <-> B = D))

Syntax hints:   -> wi 4   <-> wb 176   /\ wa 358   = wceq 1642

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-11 1746  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-an 360  df-ex 1542  df-cleq 2346

This theorem is referenced by:  eqeq12i  2366  eqeq12d  2367  eqeqan12d  2368  dfpw12  4302  fununiq  5518  fntxp  5805  pw1fnf1o  5856  fundmen  6044  ncdisjeq  6149  peano4nc  6151  sbth  6207  tc11  6229  fnfrec  6321