Theorem sbco2v 1964

Description: Version of sbco2 1981 with disjoint variable conditions. (Contributed by Wolf Lammen, 29-Apr-2023.)

Hypothesis

Ref	Expression
sbco2v.1	|- F/ z ph

Assertion

Ref	Expression
sbco2v	|- ( [ y / z ] [ z / x ] ph <-> [ y / x ] ph )

Distinct variable groups:   x, z   y, z

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

Proof of Theorem sbco2v

Step	Hyp	Ref	Expression
1		sbco2v.1	. . 3 |- F/ z ph
2	1	nfsbv 1963	. 2 |- F/ z [ y / x ] ph
3		sbequ 1851	. 2 |- ( z = y -> ( [ z / x ] ph <-> [ y / x ] ph ) )
4	2, 3	sbiev 1803	1 |- ( [ y / z ] [ z / x ] ph <-> [ y / x ] ph )

Syntax hints:   <-> wb 105   F/wnf 1471   [wsb 1773

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-io 710  ax-5 1458  ax-7 1459  ax-gen 1460  ax-ie1 1504  ax-ie2 1505  ax-8 1515  ax-10 1516  ax-11 1517  ax-i12 1518  ax-4 1521  ax-17 1537  ax-i9 1541  ax-ial 1545  ax-i5r 1546

This theorem depends on definitions:  df-bi 117  df-nf 1472  df-sb 1774

This theorem is referenced by: (None)