Theorem uncom 3271

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 723	. . 3 |- ( ( x e. A \/ x e. B ) <-> ( x e. B \/ x e. A ) )
2		elun 3268	. . 3 |- ( x e. ( B u. A ) <-> ( x e. B \/ x e. A ) )
3	1, 2	bitr4i 186	. 2 |- ( ( x e. A \/ x e. B ) <-> x e. ( B u. A ) )
4	3	uneqri 3269	1 |- ( A u. B ) = ( B u. A )

Syntax hints:   \/ wo 703   = wceq 1348   e. wcel 2141   u. cun 3119

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-io 704  ax-5 1440  ax-7 1441  ax-gen 1442  ax-ie1 1486  ax-ie2 1487  ax-8 1497  ax-10 1498  ax-11 1499  ax-i12 1500  ax-bndl 1502  ax-4 1503  ax-17 1519  ax-i9 1523  ax-ial 1527  ax-i5r 1528  ax-ext 2152

This theorem depends on definitions:  df-bi 116  df-tru 1351  df-nf 1454  df-sb 1756  df-clab 2157  df-cleq 2163  df-clel 2166  df-nfc 2301  df-v 2732  df-un 3125

This theorem is referenced by:  equncom  3272  uneq2  3275  un12  3285  un23  3286  ssun2  3291  unss2  3298  ssequn2  3300  undir  3377  dif32  3390  undif2ss  3490  uneqdifeqim  3500  prcom  3659  tpass  3679  prprc1  3691  difsnss  3726  suc0  4396  fvun2  5563  fmptpr  5688  fvsnun2  5694  fsnunfv  5697  omv2  6444  phplem2  6831  undifdc  6901  endjusym  7073  fzsuc2  10035  fseq1p1m1  10050  ennnfonelem1  12362  setsslid  12466  exmid1stab  14033