Theorem undif1 3625

Description: Absorption of difference by union. This decomposes a union into two disjoint classes (see disjdif 3622). Theorem 35 of [Suppes] p. 29. (Contributed by NM, 19-May-1998.)

Assertion

Ref	Expression
undif1	|- ((A \ B) u. B) = (A u. B)

Proof of Theorem undif1

Step	Hyp	Ref	Expression
1		undir 3504	. 2 |- ((A i^i (_V \ B)) u. B) = ((A u. B) i^i ((_V \ B) u. B))
2		invdif 3496	. . 3 |- (A i^i (_V \ B)) = (A \ B)
3	2	uneq1i 3414	. 2 |- ((A i^i (_V \ B)) u. B) = ((A \ B) u. B)
4		uncom 3408	. . . . 5 |- ((_V \ B) u. B) = (B u. (_V \ B))
5		undifv 3624	. . . . 5 |- (B u. (_V \ B)) = _V
6	4, 5	eqtri 2373	. . . 4 |- ((_V \ B) u. B) = _V
7	6	ineq2i 3454	. . 3 |- ((A u. B) i^i ((_V \ B) u. B)) = ((A u. B) i^i _V)
8		inv1 3577	. . 3 |- ((A u. B) i^i _V) = (A u. B)
9	7, 8	eqtri 2373	. 2 |- ((A u. B) i^i ((_V \ B) u. B)) = (A u. B)
10	1, 3, 9	3eqtr3i 2381	1 |- ((A \ B) u. B) = (A u. B)

Syntax hints:   = wceq 1642  _Vcvv 2859   \ cdif 3206   u. cun 3207   i^i cin 3208

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 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-ne 2518  df-v 2861  df-nin 3211  df-compl 3212  df-in 3213  df-un 3214  df-dif 3215  df-ss 3259  df-nul 3551

This theorem is referenced by:  undif2  3626  nnsucelrlem4  4427  ssfin  4470  sfinltfin  4535