Theorem elpr2 4199

Description: A member of an unordered pair of classes is one or the other of them. Exercise 1 of [TakeutiZaring] p. 15. (Contributed by NM, 14-Oct-2005.) (Proof shortened by JJ, 23-Jul-2021.)

Hypotheses

Ref	Expression
elpr2.1	|- B e. _V
elpr2.2	|- C e. _V

Assertion

Ref	Expression
elpr2	|- ( A e. { B , C } <-> ( A = B \/ A = C ) )

Proof of Theorem elpr2

Step	Hyp	Ref	Expression
1		elex 3212	. 2 |- ( A e. { B , C } -> A e. _V )
2		elpr2.1	. . . 4 |- B e. _V
3		eleq1 2689	. . . 4 |- ( A = B -> ( A e. _V <-> B e. _V ) )
4	2, 3	mpbiri 248	. . 3 |- ( A = B -> A e. _V )
5		elpr2.2	. . . 4 |- C e. _V
6		eleq1 2689	. . . 4 |- ( A = C -> ( A e. _V <-> C e. _V ) )
7	5, 6	mpbiri 248	. . 3 |- ( A = C -> A e. _V )
8	4, 7	jaoi 394	. 2 |- ( ( A = B \/ A = C ) -> A e. _V )
9		elprg 4196	. 2 |- ( A e. _V -> ( A e. { B , C } <-> ( A = B \/ A = C ) ) )
10	1, 8, 9	pm5.21nii 368	1 |- ( A e. { B , C } <-> ( A = B \/ A = C ) )

Syntax hints:   <-> wb 196   \/ wo 383   = wceq 1483   e. wcel 1990   _Vcvv 3200   {cpr 4179

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1722  ax-4 1737  ax-5 1839  ax-6 1888  ax-7 1935  ax-9 1999  ax-10 2019  ax-11 2034  ax-12 2047  ax-13 2246  ax-ext 2602

This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-tru 1486  df-ex 1705  df-nf 1710  df-sb 1881  df-clab 2609  df-cleq 2615  df-clel 2618  df-nfc 2753  df-v 3202  df-un 3579  df-sn 4178  df-pr 4180

This theorem is referenced by:  elopg  4934  elxr  11950  fprodex01  29571  nofv  31810