Theorem uncom 3349

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 733	. . 3 |- ( ( x e. A \/ x e. B ) <-> ( x e. B \/ x e. A ) )
2		elun 3346	. . 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 3347	1 |- ( A u. B ) = ( B u. A )

Syntax hints:   \/ wo 713   = wceq 1395   e. wcel 2200   u. cun 3196

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 714  ax-5 1493  ax-7 1494  ax-gen 1495  ax-ie1 1539  ax-ie2 1540  ax-8 1550  ax-10 1551  ax-11 1552  ax-i12 1553  ax-bndl 1555  ax-4 1556  ax-17 1572  ax-i9 1576  ax-ial 1580  ax-i5r 1581  ax-ext 2211

This theorem depends on definitions:  df-bi 117  df-tru 1398  df-nf 1507  df-sb 1809  df-clab 2216  df-cleq 2222  df-clel 2225  df-nfc 2361  df-v 2802  df-un 3202

This theorem is referenced by:  equncom  3350  uneq2  3353  un12  3363  un23  3364  ssun2  3369  unss2  3376  ssequn2  3378  undir  3455  dif32  3468  undif2ss  3568  uneqdifeqim  3578  prcom  3745  tpass  3765  prprc1  3778  difsnss  3817  exmid1stab  4296  suc0  4506  fununfun  5370  fvun2  5709  fmptpr  5841  fvsnun2  5847  fsnunfv  5850  omv2  6628  phplem2  7034  undifdc  7109  endjusym  7286  fzsuc2  10304  fseq1p1m1  10319  xnn0nnen  10689  ennnfonelem1  13018  setsslid  13123  lgsquadlem2  15797