Theorem sb4b 1224

Description: Simplified definition of substitution when variables are distinct.

Assertion

Ref	Expression
sb4b	|- (-. A.x x = y -> ([y / x]ph <-> A.x(x = y -> ph)))

Proof of Theorem sb4b

Step	Hyp	Ref	Expression
1		sb4 1223	. 2 |- (-. A.x x = y -> ([y / x]ph -> A.x(x = y -> ph)))
2		sb2 1177	. 2 |- (A.x(x = y -> ph) -> [y / x]ph)
3	1, 2	impbid1 517	1 |- (-. A.x x = y -> ([y / x]ph <-> A.x(x = y -> ph)))

Syntax hints:  -. wn 2   -> wi 3   <-> wb 146  A.wal 954   = wceq 956  [wsbc 1170

This theorem is referenced by:  sbcom 1258  sbcom2 1334

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7  ax-7 962  ax-gen 963  ax-10 966  ax-12 968  ax-4 973  ax-5o 975  ax-6o 978  ax-9o 1123  ax-10o 1140  ax-11o 1218

This theorem depends on definitions:  df-bi 147  df-an 225  df-ex 981  df-sb 1172

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