Theorem hbs1 1967

Description: x is not free in [ y / x ] ph when x and y are distinct. (Contributed by NM, 5-Aug-1993.) (Proof by Jim Kingdon, 16-Dec-2017.) (New usage is discouraged.)

Assertion

Ref	Expression
hbs1	|- ( [ y / x ] ph -> A. x [ y / x ] ph )

Distinct variable group:   x, y

Allowed substitution hints:   ph( x, y)

Proof of Theorem hbs1

Step	Hyp	Ref	Expression
1		sb6 1911	. 2 |- ( [ y / x ] ph <-> A. x ( x = y -> ph ) )
2		ax-ial 1558	. 2 |- ( A. x ( x = y -> ph ) -> A. x A. x ( x = y -> ph ) )
3	1, 2	hbxfrbi 1496	1 |- ( [ y / x ] ph -> A. x [ y / x ] ph )

Syntax hints:   -> wi 4   A.wal 1371   [wsb 1786

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-5 1471  ax-gen 1473  ax-ie1 1517  ax-ie2 1518  ax-8 1528  ax-11 1530  ax-4 1534  ax-17 1550  ax-i9 1554  ax-ial 1558

This theorem depends on definitions:  df-bi 117  df-sb 1787

This theorem is referenced by:  nfs1v  1968  sb9v  2007  eu1  2080  mopick  2134  hbab1  2196