Theorem ax16 1735

Description: Theorem showing that ax-16 1736 is redundant if ax-17 1460 is included in the axiom system. The important part of the proof is provided by aev 1734.

See ax16ALT 1781 for an alternate proof that does not require ax-10 1437 or ax-12 1443.

This theorem should not be referenced in any proof. Instead, use ax-16 1736 below so that theorems needing ax-16 1736 can be more easily identified. (Contributed by NM, 8-Nov-2006.)

Assertion

Ref	Expression
ax16	|- ( A. x x = y -> ( ph -> A. x ph ) )

Distinct variable group:   x, y

Allowed substitution hints:   ph( x, y)

Proof of Theorem ax16

Dummy variable z is distinct from all other variables.

Step	Hyp	Ref	Expression
1		aev 1734	. 2 |- ( A. x x = y -> A. z x = z )
2		ax-17 1460	. . . 4 |- ( ph -> A. z ph )
3		sbequ12 1695	. . . . 5 |- ( x = z -> ( ph <-> [ z / x ] ph ) )
4	3	biimpcd 157	. . . 4 |- ( ph -> ( x = z -> [ z / x ] ph ) )
5	2, 4	alimdh 1397	. . 3 |- ( ph -> ( A. z x = z -> A. z [ z / x ] ph ) )
6	2	hbsb3 1730	. . . 4 |- ( [ z / x ] ph -> A. x [ z / x ] ph )
7		stdpc7 1694	. . . 4 |- ( z = x -> ( [ z / x ] ph -> ph ) )
8	6, 2, 7	cbv3h 1672	. . 3 |- ( A. z [ z / x ] ph -> A. x ph )
9	5, 8	syl6com 35	. 2 |- ( A. z x = z -> ( ph -> A. x ph ) )
10	1, 9	syl 14	1 |- ( A. x x = y -> ( ph -> A. x ph ) )

Syntax hints:   -> wi 4   A.wal 1283   [wsb 1686

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-io 663  ax-5 1377  ax-7 1378  ax-gen 1379  ax-ie1 1423  ax-ie2 1424  ax-8 1436  ax-10 1437  ax-11 1438  ax-i12 1439  ax-4 1441  ax-17 1460  ax-i9 1464  ax-ial 1468

This theorem depends on definitions:  df-bi 115  df-nf 1391  df-sb 1687

This theorem is referenced by:  dveeq2  1737  dveeq2or  1738  a16g  1786  exists2  2039