Theorem hbs1f 1774

Description: If x is not free in ph, it is not free in [ y / x ] ph. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 25-May-2011.)

Hypothesis

Ref	Expression
hbs1f.1	|- ( ph -> A. x ph )

Assertion

Ref	Expression
hbs1f	|- ( [ y / x ] ph -> A. x [ y / x ] ph )

Proof of Theorem hbs1f

Step	Hyp	Ref	Expression
1		hbs1f.1	. . 3 |- ( ph -> A. x ph )
2	1	sbh 1769	. 2 |- ( [ y / x ] ph <-> ph )
3	2, 1	hbxfrbi 1465	1 |- ( [ y / x ] ph -> A. x [ y / x ] ph )

Syntax hints:   -> wi 4   A.wal 1346   [wsb 1755

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-5 1440  ax-gen 1442  ax-ie1 1486  ax-ie2 1487  ax-4 1503  ax-i9 1523  ax-ial 1527

This theorem depends on definitions:  df-bi 116  df-sb 1756

This theorem is referenced by: (None)