Theorem 19.3 1486

Description: A wff may be quantified with a variable not free in it. Theorem 19.3 of [Margaris] p. 89. (Contributed by NM, 5-Aug-1993.) (Revised by Mario Carneiro, 24-Sep-2016.)

Hypothesis

Ref	Expression
19.3.1	|- F/ x ph

Assertion

Ref	Expression
19.3	|- ( A. x ph <-> ph )

Proof of Theorem 19.3

Step	Hyp	Ref	Expression
1		sp 1441	. 2 |- ( A. x ph -> ph )
2		19.3.1	. . 3 |- F/ x ph
3	2	nfri 1452	. 2 |- ( ph -> A. x ph )
4	1, 3	impbii 124	1 |- ( A. x ph <-> ph )

Syntax hints:   <-> wb 103   A.wal 1282   F/wnf 1389

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-4 1440

This theorem depends on definitions:  df-bi 115  df-nf 1390

This theorem is referenced by:  19.16  1487  19.17  1488  19.27  1493  19.28  1495  19.37-1  1604  rexxfrd  4213