Theorem elprg 3729

Description: A member of an unordered pair of classes is one or the other of them. Exercise 1 of [TakeutiZaring] p. 15, generalized. (Contributed by NM, 13-Sep-1995.)

Assertion

Ref	Expression
elprg	|- ( A e. V -> ( A e. { B , C } <-> ( A = B \/ A = C ) ) )

Proof of Theorem elprg

Dummy variable x is distinct from all other variables.

Step	Hyp	Ref	Expression
1		eqeq1 2245	. . 3 |- ( x = A -> ( x = B <-> A = B ) )
2		eqeq1 2245	. . 3 |- ( x = A -> ( x = C <-> A = C ) )
3	1, 2	orbi12d 805	. 2 |- ( x = A -> ( ( x = B \/ x = C ) <-> ( A = B \/ A = C ) ) )
4		dfpr2 3728	. 2 |- { B , C } = { x | ( x = B \/ x = C ) }
5	3, 4	elab2g 2973	1 |- ( A e. V -> ( A e. { B , C } <-> ( A = B \/ A = C ) ) )

This proof depends on syntax axioms:   -> wi 4   <-> wb 105   \/ wo 720   = wceq 1402   e. wcel 2209   {cpr 3710

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 721  ax-5 1500  ax-7 1501  ax-gen 1502  ax-ie1 1546  ax-ie2 1547  ax-8 1557  ax-10 1558  ax-11 1559  ax-i12 1560  ax-bndl 1562  ax-4 1563  ax-17 1579  ax-i9 1583  ax-ial 1587  ax-i5r 1588  ax-ext 2220

This proof depends on definitions:  df-bi 117  df-tru 1405  df-nf 1514  df-sb 1816  df-clab 2225  df-cleq 2231  df-clel 2234  df-nfc 2381  df-v 2823  df-un 3224  df-sn 3715  df-pr 3716

This theorem is used by:  elpr  3730  elpr2  3731  elpri  3732  eldifpr  3736  eltpg  3754  prid1g  3815  ssprss  3876  preqr1g  3891  m1expeven  11038  maxclpr  12005  minmax  12014  minclpr  12021  xrminmax  12050  ppiqub  16254  perfectlem2  16261  lgslem1  16285  lgsval  16289  lgsfvalg  16290  lgsfcl2  16291  lgsval2lem  16295  lgsdir2lem4  16316  lgsdir2lem5  16317  lgsdir2  16318  lgsne0  16323  gausslemma2dlem0i  16342  2lgs  16389  2lgsoddprm  16398  eupth2lem1  16865  eupth2lem3lem4fi  16880