Theorem exsb 1352

Description: An equivalent expression for existence.

Assertion

Ref	Expression
exsb	|- (E.xph <-> E.yA.x(x = y -> ph))

Distinct variable groups:   x,y   ph,y

Proof of Theorem exsb

Step	Hyp	Ref	Expression
1		ax-17 973	. . 3 |- (ph -> A.yph)
2	1	sb8e 1264	. 2 |- (E.xph <-> E.y[y / x]ph)
3		sb6 1269	. . 3 |- ([y / x]ph <-> A.x(x = y -> ph))
4	3	exbii 1053	. 2 |- (E.y[y / x]ph <-> E.yA.x(x = y -> ph))
5	2, 4	bitr 173	1 |- (E.xph <-> E.yA.x(x = y -> ph))

Syntax hints:   -> wi 3   <-> wb 146  A.wal 956   = wceq 958  E.wex 982

This theorem is referenced by:  2exsb 1353

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7  ax-7 964  ax-gen 965  ax-8 966  ax-10 968  ax-11 969  ax-12 970  ax-17 973  ax-4 975  ax-5o 977  ax-6o 980  ax-9o 1125  ax-10o 1142  ax-16 1212  ax-11o 1220

This theorem depends on definitions:  df-bi 147  df-or 224  df-an 225  df-ex 983  df-sb 1174

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