Theorem eqvincf 2720

Description: A variable introduction law for class equality, using bound-variable hypotheses instead of distinct variable conditions. (Contributed by NM, 14-Sep-2003.)

Hypotheses

Ref	Expression
eqvincf.1	|- F/_ x A
eqvincf.2	|- F/_ x B
eqvincf.3	|- A e. _V

Assertion

Ref	Expression
eqvincf	|- ( A = B <-> E. x ( x = A /\ x = B ) )

Proof of Theorem eqvincf

Dummy variable y is distinct from all other variables.

Step	Hyp	Ref	Expression
1		eqvincf.3	. . 3 |- A e. _V
2	1	eqvinc 2718	. 2 |- ( A = B <-> E. y ( y = A /\ y = B ) )
3		eqvincf.1	. . . . 5 |- F/_ x A
4	3	nfeq2 2230	. . . 4 |- F/ x y = A
5		eqvincf.2	. . . . 5 |- F/_ x B
6	5	nfeq2 2230	. . . 4 |- F/ x y = B
7	4, 6	nfan 1497	. . 3 |- F/ x ( y = A /\ y = B )
8		nfv 1461	. . 3 |- F/ y ( x = A /\ x = B )
9		eqeq1 2087	. . . 4 |- ( y = x -> ( y = A <-> x = A ) )
10		eqeq1 2087	. . . 4 |- ( y = x -> ( y = B <-> x = B ) )
11	9, 10	anbi12d 456	. . 3 |- ( y = x -> ( ( y = A /\ y = B ) <-> ( x = A /\ x = B ) ) )
12	7, 8, 11	cbvex 1679	. 2 |- ( E. y ( y = A /\ y = B ) <-> E. x ( x = A /\ x = B ) )
13	2, 12	bitri 182	1 |- ( A = B <-> E. x ( x = A /\ x = B ) )

Syntax hints:   /\ wa 102   <-> wb 103   = wceq 1284   E.wex 1421   e. wcel 1433   F/_wnfc 2206   _Vcvv 2601

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-io 662  ax-5 1376  ax-7 1377  ax-gen 1378  ax-ie1 1422  ax-ie2 1423  ax-8 1435  ax-10 1436  ax-11 1437  ax-i12 1438  ax-bndl 1439  ax-4 1440  ax-17 1459  ax-i9 1463  ax-ial 1467  ax-i5r 1468  ax-ext 2063

This theorem depends on definitions:  df-bi 115  df-tru 1287  df-nf 1390  df-sb 1686  df-clab 2068  df-cleq 2074  df-clel 2077  df-nfc 2208  df-v 2603

This theorem is referenced by: (None)