Theorem difeq1 3246

Description: Equality theorem for class difference. (Contributed by NM, 10-Feb-1997.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)

Assertion

Ref	Expression
difeq1	⊢ (A = B → (A ∖ C) = (B ∖ C))

Proof of Theorem difeq1

Step	Hyp	Ref	Expression
1		nineq1 3234	. . 3 ⊢ (A = B → (A ⩃ ∼ C) = (B ⩃ ∼ C))
2	1	compleqd 3245	. 2 ⊢ (A = B → ∼ (A ⩃ ∼ C) = ∼ (B ⩃ ∼ C))
3		df-dif 3215	. . 3 ⊢ (A ∖ C) = (A ∩ ∼ C)
4		df-in 3213	. . 3 ⊢ (A ∩ ∼ C) = ∼ (A ⩃ ∼ C)
5	3, 4	eqtri 2373	. 2 ⊢ (A ∖ C) = ∼ (A ⩃ ∼ C)
6		df-dif 3215	. . 3 ⊢ (B ∖ C) = (B ∩ ∼ C)
7		df-in 3213	. . 3 ⊢ (B ∩ ∼ C) = ∼ (B ⩃ ∼ C)
8	6, 7	eqtri 2373	. 2 ⊢ (B ∖ C) = ∼ (B ⩃ ∼ C)
9	2, 5, 8	3eqtr4g 2410	1 ⊢ (A = B → (A ∖ C) = (B ∖ C))

Syntax hints:   → wi 4   = wceq 1642   ⩃ cnin 3204   ∼ ccompl 3205   ∖ cdif 3206   ∩ cin 3208

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2478  df-v 2861  df-nin 3211  df-compl 3212  df-in 3213  df-dif 3215

This theorem is referenced by:  symdifeq1  3248  symdifeq2  3249  difeq12  3380  difeq1i  3381  difeq1d  3384  uneqdifeq  3638  adj11  3889