Theorem undif1ss 3483

Description: Absorption of difference by union. In classical logic, as Theorem 35 of [Suppes] p. 29, this would be equality rather than subset. (Contributed by Jim Kingdon, 4-Aug-2018.)

Assertion

Ref	Expression
undif1ss	|- ( ( A \ B ) u. B ) C_ ( A u. B )

Proof of Theorem undif1ss

Step	Hyp	Ref	Expression
1		difss 3248	. 2 |- ( A \ B ) C_ A
2		unss1 3291	. 2 |- ( ( A \ B ) C_ A -> ( ( A \ B ) u. B ) C_ ( A u. B ) )
3	1, 2	ax-mp 5	1 |- ( ( A \ B ) u. B ) C_ ( A u. B )

Syntax hints:   \ cdif 3113   u. cun 3114   C_ wss 3116

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 1435  ax-7 1436  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-8 1492  ax-10 1493  ax-11 1494  ax-i12 1495  ax-bndl 1497  ax-4 1498  ax-17 1514  ax-i9 1518  ax-ial 1522  ax-i5r 1523  ax-ext 2147

This theorem depends on definitions:  df-bi 116  df-tru 1346  df-nf 1449  df-sb 1751  df-clab 2152  df-cleq 2158  df-clel 2161  df-nfc 2297  df-v 2728  df-dif 3118  df-un 3120  df-in 3122  df-ss 3129

This theorem is referenced by:  undif2ss  3484  pwundifss  4263