Theorem sbid 1704

Description: An identity theorem for substitution. Remark 9.1 in [Megill] p. 447 (p. 15 of the preprint). (Contributed by NM, 5-Aug-1993.)

Assertion

Ref	Expression
sbid	|- ( [ x / x ] ph <-> ph )

Proof of Theorem sbid

Step	Hyp	Ref	Expression
1		equid 1634	. . 3 |- x = x
2		sbequ12 1701	. . 3 |- ( x = x -> ( ph <-> [ x / x ] ph ) )
3	1, 2	ax-mp 7	. 2 |- ( ph <-> [ x / x ] ph )
4	3	bicomi 130	1 |- ( [ x / x ] ph <-> ph )

Syntax hints:   <-> wb 103   [wsb 1692

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-gen 1383  ax-ie1 1427  ax-ie2 1428  ax-8 1440  ax-4 1445  ax-17 1464  ax-i9 1468

This theorem depends on definitions:  df-bi 115  df-sb 1693

This theorem is referenced by:  abid  2076  sbceq1a  2849  sbcid  2855