Theorem nfs1 1797

Description: If y is not free in ph, x is not free in [ y / x ] ph. (Contributed by Mario Carneiro, 11-Aug-2016.)

Hypothesis

Ref	Expression
nfs1.1	|- F/ y ph

Assertion

Ref	Expression
nfs1	|- F/ x [ y / x ] ph

Proof of Theorem nfs1

Step	Hyp	Ref	Expression
1		nfs1.1	. . . 4 |- F/ y ph
2	1	nfri 1507	. . 3 |- ( ph -> A. y ph )
3	2	hbsb3 1796	. 2 |- ( [ y / x ] ph -> A. x [ y / x ] ph )
4	3	nfi 1450	1 |- F/ x [ y / x ] ph

Syntax hints:   F/wnf 1448   [wsb 1750

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 1435  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-11 1494  ax-4 1498  ax-i9 1518  ax-ial 1522

This theorem depends on definitions:  df-bi 116  df-nf 1449  df-sb 1751

This theorem is referenced by:  sb8  1844  sb8e  1845