Theorem sbcom2 1938

Description: Commutativity law for substitution. Used in proof of Theorem 9.7 of [Megill] p. 449 (p. 16 of the preprint). (Contributed by NM, 27-May-1997.) (Proof modified to be intuitionistic by Jim Kingdon, 19-Feb-2018.)

Assertion

Ref	Expression
sbcom2	|- ( [ w / z ] [ y / x ] ph <-> [ y / x ] [ w / z ] ph )

Distinct variable groups:   x, z   x, w   y, z

Allowed substitution hints:   ph( x, y, z, w)

Proof of Theorem sbcom2

Dummy variable v is distinct from all other variables.

Step	Hyp	Ref	Expression
1		sbcom2v2 1937	. . . 4 |- ( [ v / z ] [ y / x ] ph <-> [ y / x ] [ v / z ] ph )
2	1	sbbii 1721	. . 3 |- ( [ w / v ] [ v / z ] [ y / x ] ph <-> [ w / v ] [ y / x ] [ v / z ] ph )
3		sbcom2v2 1937	. . 3 |- ( [ w / v ] [ y / x ] [ v / z ] ph <-> [ y / x ] [ w / v ] [ v / z ] ph )
4	2, 3	bitri 183	. 2 |- ( [ w / v ] [ v / z ] [ y / x ] ph <-> [ y / x ] [ w / v ] [ v / z ] ph )
5		ax-17 1489	. . 3 |- ( [ y / x ] ph -> A. v [ y / x ] ph )
6	5	sbco2v 1896	. 2 |- ( [ w / v ] [ v / z ] [ y / x ] ph <-> [ w / z ] [ y / x ] ph )
7		ax-17 1489	. . . 4 |- ( ph -> A. v ph )
8	7	sbco2v 1896	. . 3 |- ( [ w / v ] [ v / z ] ph <-> [ w / z ] ph )
9	8	sbbii 1721	. 2 |- ( [ y / x ] [ w / v ] [ v / z ] ph <-> [ y / x ] [ w / z ] ph )
10	4, 6, 9	3bitr3i 209	1 |- ( [ w / z ] [ y / x ] ph <-> [ y / x ] [ w / z ] ph )

Syntax hints:   <-> wb 104   [wsb 1718

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-io 681  ax-5 1406  ax-7 1407  ax-gen 1408  ax-ie1 1452  ax-ie2 1453  ax-8 1465  ax-10 1466  ax-11 1467  ax-i12 1468  ax-4 1470  ax-17 1489  ax-i9 1493  ax-ial 1497  ax-i5r 1498

This theorem depends on definitions:  df-bi 116  df-nf 1420  df-sb 1719

This theorem is referenced by:  2sb5rf  1940  2sb6rf  1941  sbco4lem  1957  sbco4  1958  sbmo  2034  cnvopab  4898