Theorem sbco4 2035

Description: Two ways of exchanging two variables. Both sides of the biconditional exchange x and y, either via two temporary variables u and v, or a single temporary w. (Contributed by Jim Kingdon, 25-Sep-2018.)

Assertion

Ref	Expression
sbco4	|- ( [ y / u ] [ x / v ] [ u / x ] [ v / y ] ph <-> [ x / w ] [ y / x ] [ w / y ] ph )

Distinct variable groups:   v, u, ph   x, u, v   y, u, v   ph, w   x, w   y, w

Allowed substitution hints:   ph( x, y)

Proof of Theorem sbco4

Dummy variable t is distinct from all other variables.

Step	Hyp	Ref	Expression
1		sbcom2 2015	. . 3 |- ( [ x / v ] [ y / u ] [ u / x ] [ v / y ] ph <-> [ y / u ] [ x / v ] [ u / x ] [ v / y ] ph )
2		nfv 1551	. . . . 5 |- F/ u [ v / y ] ph
3	2	sbco2 1993	. . . 4 |- ( [ y / u ] [ u / x ] [ v / y ] ph <-> [ y / x ] [ v / y ] ph )
4	3	sbbii 1788	. . 3 |- ( [ x / v ] [ y / u ] [ u / x ] [ v / y ] ph <-> [ x / v ] [ y / x ] [ v / y ] ph )
5	1, 4	bitr3i 186	. 2 |- ( [ y / u ] [ x / v ] [ u / x ] [ v / y ] ph <-> [ x / v ] [ y / x ] [ v / y ] ph )
6		sbco4lem 2034	. 2 |- ( [ x / v ] [ y / x ] [ v / y ] ph <-> [ x / t ] [ y / x ] [ t / y ] ph )
7		sbco4lem 2034	. 2 |- ( [ x / t ] [ y / x ] [ t / y ] ph <-> [ x / w ] [ y / x ] [ w / y ] ph )
8	5, 6, 7	3bitri 206	1 |- ( [ y / u ] [ x / v ] [ u / x ] [ v / y ] ph <-> [ x / w ] [ y / x ] [ w / y ] ph )

Syntax hints:   <-> wb 105   [wsb 1785

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 711  ax-5 1470  ax-7 1471  ax-gen 1472  ax-ie1 1516  ax-ie2 1517  ax-8 1527  ax-10 1528  ax-11 1529  ax-i12 1530  ax-bndl 1532  ax-4 1533  ax-17 1549  ax-i9 1553  ax-ial 1557  ax-i5r 1558

This theorem depends on definitions:  df-bi 117  df-nf 1484  df-sb 1786

This theorem is referenced by: (None)