Theorem uncom 3304

Description: Commutative law for union of classes. Exercise 6 of [TakeutiZaring] p. 17. (Contributed by NM, 25-Jun-1998.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)

Assertion

Ref	Expression
uncom	|- ( A u. B ) = ( B u. A )

Proof of Theorem uncom

Dummy variable x is distinct from all other variables.

Step	Hyp	Ref	Expression
1		orcom 729	. . 3 |- ( ( x e. A \/ x e. B ) <-> ( x e. B \/ x e. A ) )
2		elun 3301	. . 3 |- ( x e. ( B u. A ) <-> ( x e. B \/ x e. A ) )
3	1, 2	bitr4i 187	. 2 |- ( ( x e. A \/ x e. B ) <-> x e. ( B u. A ) )
4	3	uneqri 3302	1 |- ( A u. B ) = ( B u. A )

Syntax hints:   \/ wo 709   = wceq 1364   e. wcel 2164   u. cun 3152

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-io 710  ax-5 1458  ax-7 1459  ax-gen 1460  ax-ie1 1504  ax-ie2 1505  ax-8 1515  ax-10 1516  ax-11 1517  ax-i12 1518  ax-bndl 1520  ax-4 1521  ax-17 1537  ax-i9 1541  ax-ial 1545  ax-i5r 1546  ax-ext 2175

This theorem depends on definitions:  df-bi 117  df-tru 1367  df-nf 1472  df-sb 1774  df-clab 2180  df-cleq 2186  df-clel 2189  df-nfc 2325  df-v 2762  df-un 3158

This theorem is referenced by:  equncom  3305  uneq2  3308  un12  3318  un23  3319  ssun2  3324  unss2  3331  ssequn2  3333  undir  3410  dif32  3423  undif2ss  3523  uneqdifeqim  3533  prcom  3695  tpass  3715  prprc1  3727  difsnss  3765  exmid1stab  4238  suc0  4443  fvun2  5625  fmptpr  5751  fvsnun2  5757  fsnunfv  5760  omv2  6520  phplem2  6911  undifdc  6982  endjusym  7157  fzsuc2  10148  fseq1p1m1  10163  xnn0nnen  10511  ennnfonelem1  12567  setsslid  12672  lgsquadlem2  15235