Theorem uncom 3348

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 3345	. . 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 3346	1 |- ( A u. B ) = ( B u. A )

Syntax hints:   \/ wo 713   = wceq 1395   e. wcel 2200   u. cun 3195

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 2801  df-un 3201

This theorem is referenced by:  equncom  3349  uneq2  3352  un12  3362  un23  3363  ssun2  3368  unss2  3375  ssequn2  3377  undir  3454  dif32  3467  undif2ss  3567  uneqdifeqim  3577  prcom  3742  tpass  3762  prprc1  3775  difsnss  3814  exmid1stab  4292  suc0  4502  fununfun  5364  fvun2  5703  fmptpr  5835  fvsnun2  5841  fsnunfv  5844  omv2  6619  phplem2  7022  undifdc  7097  endjusym  7274  fzsuc2  10287  fseq1p1m1  10302  xnn0nnen  10671  ennnfonelem1  12994  setsslid  13099  lgsquadlem2  15773