Theorem sb5f 1827

Description: Equivalence for substitution when y is not free in ph. (Contributed by NM, 5-Aug-1993.) (Revised by NM, 18-May-2008.)

Hypothesis

Ref	Expression
equs45f.1	|- ( ph -> A. y ph )

Assertion

Ref	Expression
sb5f	|- ( [ y / x ] ph <-> E. x ( x = y /\ ph ) )

Proof of Theorem sb5f

Step	Hyp	Ref	Expression
1		equs45f.1	. . 3 |- ( ph -> A. y ph )
2	1	sb6f 1826	. 2 |- ( [ y / x ] ph <-> A. x ( x = y -> ph ) )
3	1	equs45f 1825	. 2 |- ( E. x ( x = y /\ ph ) <-> A. x ( x = y -> ph ) )
4	2, 3	bitr4i 187	1 |- ( [ y / x ] ph <-> E. x ( x = y /\ ph ) )

Syntax hints:   -> wi 4   /\ wa 104   <-> wb 105   A.wal 1371   E.wex 1515   [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-11 1529  ax-4 1533  ax-i9 1553  ax-ial 1557

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

This theorem is referenced by:  sbcof2  1833