Theorem dif0 3433

Description: The difference between a class and the empty set. Part of Exercise 4.4 of [Stoll] p. 16. (Contributed by NM, 17-Aug-2004.)

Assertion

Ref	Expression
dif0	⊢ (𝐴 ∖ ∅) = 𝐴

Proof of Theorem dif0

Step	Hyp	Ref	Expression
1		difid 3431	. . 3 ⊢ (𝐴 ∖ 𝐴) = ∅
2	1	difeq2i 3191	. 2 ⊢ (𝐴 ∖ (𝐴 ∖ 𝐴)) = (𝐴 ∖ ∅)
3		difdif 3201	. 2 ⊢ (𝐴 ∖ (𝐴 ∖ 𝐴)) = 𝐴
4	2, 3	eqtr3i 2162	1 ⊢ (𝐴 ∖ ∅) = 𝐴

Syntax hints:   = wceq 1331   ∖ cdif 3068  ∅c0 3363

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 603  ax-in2 604  ax-io 698  ax-5 1423  ax-7 1424  ax-gen 1425  ax-ie1 1469  ax-ie2 1470  ax-8 1482  ax-10 1483  ax-11 1484  ax-i12 1485  ax-bndl 1486  ax-4 1487  ax-17 1506  ax-i9 1510  ax-ial 1514  ax-i5r 1515  ax-ext 2121

This theorem depends on definitions:  df-bi 116  df-tru 1334  df-nf 1437  df-sb 1736  df-clab 2126  df-cleq 2132  df-clel 2135  df-nfc 2270  df-ral 2421  df-rab 2425  df-v 2688  df-dif 3073  df-in 3077  df-ss 3084  df-nul 3364

This theorem is referenced by:  disjdif2  3441  2oconcl  6336  diffifi  6788  undifdc  6812  difinfinf  6986  ismkvnex  7029  0cld  12281  exmid1stab  13195