Theorem difabs 3428

Description: Absorption-like law for class difference: you can remove a class only once. (Contributed by FL, 2-Aug-2009.)

Assertion

Ref	Expression
difabs	|- ( ( A \ B ) \ B ) = ( A \ B )

Proof of Theorem difabs

Step	Hyp	Ref	Expression
1		difun1 3424	. 2 |- ( A \ ( B u. B ) ) = ( ( A \ B ) \ B )
2		unidm 3307	. . 3 |- ( B u. B ) = B
3	2	difeq2i 3279	. 2 |- ( A \ ( B u. B ) ) = ( A \ B )
4	1, 3	eqtr3i 2219	1 |- ( ( A \ B ) \ B ) = ( A \ B )

Syntax hints:   = wceq 1364   \ cdif 3154   u. cun 3155

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-in1 615  ax-in2 616  ax-io 710  ax-5 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-10 1519  ax-11 1520  ax-i12 1521  ax-bndl 1523  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548  ax-i5r 1549  ax-ext 2178

This theorem depends on definitions:  df-bi 117  df-tru 1367  df-nf 1475  df-sb 1777  df-clab 2183  df-cleq 2189  df-clel 2192  df-nfc 2328  df-ral 2480  df-rab 2484  df-v 2765  df-dif 3159  df-un 3161  df-in 3163

This theorem is referenced by: (None)