Theorem difabs 3345

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 3341	. 2 |- ( A \ ( B u. B ) ) = ( ( A \ B ) \ B )
2		unidm 3224	. . 3 |- ( B u. B ) = B
3	2	difeq2i 3196	. 2 |- ( A \ ( B u. B ) ) = ( A \ B )
4	1, 3	eqtr3i 2163	1 |- ( ( A \ B ) \ B ) = ( A \ B )

Syntax hints:   = wceq 1332   \ cdif 3073   u. cun 3074

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 604  ax-in2 605  ax-io 699  ax-5 1424  ax-7 1425  ax-gen 1426  ax-ie1 1470  ax-ie2 1471  ax-8 1483  ax-10 1484  ax-11 1485  ax-i12 1486  ax-bndl 1487  ax-4 1488  ax-17 1507  ax-i9 1511  ax-ial 1515  ax-i5r 1516  ax-ext 2122

This theorem depends on definitions:  df-bi 116  df-tru 1335  df-nf 1438  df-sb 1737  df-clab 2127  df-cleq 2133  df-clel 2136  df-nfc 2271  df-ral 2422  df-rab 2426  df-v 2691  df-dif 3078  df-un 3080  df-in 3082

This theorem is referenced by: (None)