Theorem uncom 3353

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 736	. . 3 |- ( ( x e. A \/ x e. B ) <-> ( x e. B \/ x e. A ) )
2		elun 3350	. . 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 3351	1 |- ( A u. B ) = ( B u. A )

Syntax hints:   \/ wo 716   = wceq 1398   e. wcel 2202   u. cun 3199

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 717  ax-5 1496  ax-7 1497  ax-gen 1498  ax-ie1 1542  ax-ie2 1543  ax-8 1553  ax-10 1554  ax-11 1555  ax-i12 1556  ax-bndl 1558  ax-4 1559  ax-17 1575  ax-i9 1579  ax-ial 1583  ax-i5r 1584  ax-ext 2213

This theorem depends on definitions:  df-bi 117  df-tru 1401  df-nf 1510  df-sb 1811  df-clab 2218  df-cleq 2224  df-clel 2227  df-nfc 2364  df-v 2805  df-un 3205

This theorem is referenced by:  equncom  3354  uneq2  3357  un12  3367  un23  3368  ssun2  3373  unss2  3380  ssequn2  3382  undir  3459  dif32  3472  undif2ss  3572  uneqdifeqim  3582  prcom  3751  tpass  3771  prprc1  3784  difsnss  3824  exmid1stab  4304  suc0  4514  fununfun  5380  fvun2  5722  fmptpr  5854  fvsnun2  5860  fsnunfv  5863  omv2  6676  phplem2  7082  undifdc  7159  endjusym  7355  fzsuc2  10376  fseq1p1m1  10391  xnn0nnen  10762  ennnfonelem1  13108  setsslid  13213  lgsquadlem2  15897