Theorem exiftruOLD 1658

Description: Obsolete proof of exiftru 1657 as of 9-Dec-2017. (Contributed by Wolf Lammen, 12-Nov-2017.) (Proof modification is discouraged.) (New usage is discouraged.)

Hypothesis

Ref	Expression
exiftruOLD.1	|- ph

Assertion

Ref	Expression
exiftruOLD	|- E.xph

Proof of Theorem exiftruOLD

Dummy variable y is distinct from all other variables.

Step	Hyp	Ref	Expression
1		a9ev 1656	. . . 4 |- E.x x = y
2	1	a1i 10	. . 3 |- (A.x x = y -> E.x x = y)
3	2	19.35ri 1602	. 2 |- E.x(x = y -> x = y)
4		exiftruOLD.1	. . . 4 |- ph
5		id 19	. . . 4 |- (x = y -> x = y)
6	4, 5	2th 230	. . 3 |- (ph <-> (x = y -> x = y))
7	6	exbii 1582	. 2 |- (E.xph <-> E.x(x = y -> x = y))
8	3, 7	mpbir 200	1 |- E.xph

Syntax hints:   -> wi 4  A.wal 1540  E.wex 1541

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-9 1654

This theorem depends on definitions:  df-bi 177  df-an 360  df-ex 1542

This theorem is referenced by: (None)