Theorem sb6rf 1876

Description: Reversed substitution. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 25-May-2011.)

Hypothesis

Ref	Expression
sb5rf.1	|- ( ph -> A. y ph )

Assertion

Ref	Expression
sb6rf	|- ( ph <-> A. y ( y = x -> [ y / x ] ph ) )

Proof of Theorem sb6rf

Step	Hyp	Ref	Expression
1		sb5rf.1	. . 3 |- ( ph -> A. y ph )
2		sbequ1 1791	. . . . 5 |- ( x = y -> ( ph -> [ y / x ] ph ) )
3	2	equcoms 1731	. . . 4 |- ( y = x -> ( ph -> [ y / x ] ph ) )
4	3	com12 30	. . 3 |- ( ph -> ( y = x -> [ y / x ] ph ) )
5	1, 4	alrimih 1492	. 2 |- ( ph -> A. y ( y = x -> [ y / x ] ph ) )
6		sb2 1790	. . 3 |- ( A. y ( y = x -> [ y / x ] ph ) -> [ x / y ] [ y / x ] ph )
7	1	sbid2h 1872	. . 3 |- ( [ x / y ] [ y / x ] ph <-> ph )
8	6, 7	sylib 122	. 2 |- ( A. y ( y = x -> [ y / x ] ph ) -> ph )
9	5, 8	impbii 126	1 |- ( ph <-> A. y ( y = x -> [ y / x ] ph ) )

Syntax hints:   -> wi 4   <-> wb 105   A.wal 1371   [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-5 1470  ax-gen 1472  ax-ie1 1516  ax-ie2 1517  ax-8 1527  ax-11 1529  ax-4 1533  ax-17 1549  ax-i9 1553  ax-ial 1557

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

This theorem is referenced by:  2sb6rf  2018  eu1  2079