Theorem equs4 1133

Description: Lemma used in proofs of substitution properties.

Assertion

Ref	Expression
equs4	|- (A.x(x = y -> ph) -> E.x(x = y /\ ph))

Proof of Theorem equs4

Step	Hyp	Ref	Expression
1		pm3.27 323	. . . . . . . 8 |- ((A.x(x = y -> ph) /\ x = y) -> x = y)
2		ax-4 951	. . . . . . . . 9 |- (A.x(x = y -> ph) -> (x = y -> ph))
3	2	imp 350	. . . . . . . 8 |- ((A.x(x = y -> ph) /\ x = y) -> ph)
4	1, 3	jc 138	. . . . . . 7 |- ((A.x(x = y -> ph) /\ x = y) -> -. (x = y -> -. ph))
5		ax-4 951	. . . . . . 7 |- (A.x(x = y -> -. ph) -> (x = y -> -. ph))
6	4, 5	nsyl 116	. . . . . 6 |- ((A.x(x = y -> ph) /\ x = y) -> -. A.x(x = y -> -. ph))
7	6	ex 373	. . . . 5 |- (A.x(x = y -> ph) -> (x = y -> -. A.x(x = y -> -. ph)))
8		hbn1 989	. . . . 5 |- (-. A.x(x = y -> -. ph) -> A.x -. A.x(x = y -> -. ph))
9	7, 8	syl6 22	. . . 4 |- (A.x(x = y -> ph) -> (x = y -> A.x -. A.x(x = y -> -. ph)))
10	9	a5i 965	. . 3 |- (A.x(x = y -> ph) -> A.x(x = y -> A.x -. A.x(x = y -> -. ph)))
11		ax9 1110	. . 3 |- (A.x(x = y -> A.x -. A.x(x = y -> -. ph)) -> -. A.x(x = y -> -. ph))
12	10, 11	syl 10	. 2 |- (A.x(x = y -> ph) -> -. A.x(x = y -> -. ph))
13		equs3 1132	. 2 |- (E.x(x = y /\ ph) <-> -. A.x(x = y -> -. ph))
14	12, 13	sylibr 200	1 |- (A.x(x = y -> ph) -> E.x(x = y /\ ph))

Syntax hints:  -. wn 2   -> wi 3   /\ wa 223  A.wal 950  E.wex 956   = wceq 1099

This theorem is referenced by:  sb2 1160  equs45f 1184

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7  ax-4 951  ax-5 952  ax-6 953  ax-gen 955  ax-9 1102

This theorem depends on definitions:  df-bi 147  df-an 225  df-ex 957

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