Theorem axnulALT 3443

Description: Prove axnul 3444 directly from ax-rep 3428 without using any equality axioms (ax-9 1307 thru ax-16 1580). The wff x = x substituted for ph in the ax-rep 3428 instance is arbitrary. Here, we don't need to know if x = x is true or false, only that it's not both. (Contributed by Jeff Hoffman, 4-Feb-2008.)

Assertion

Ref	Expression
axnulALT	|- E.xA.y -. y e. x

Distinct variable group:   x,y

Proof of Theorem axnulALT

Step	Hyp	Ref	Expression
1		ax-rep 3428	. . 3 |- (A.wE.xA.y(A.x(x = x <-> -. x = x) -> y = x) -> E.xA.y(y e. x <-> E.w(w e. z /\ A.x(x = x <-> -. x = x))))
2		pm5.19 732	. . . . . . . . 9 |- -. (x = x <-> -. x = x)
3		ax-4 1319	. . . . . . . . 9 |- (A.x(x = x <-> -. x = x) -> (x = x <-> -. x = x))
4	2, 3	mto 121	. . . . . . . 8 |- -. A.x(x = x <-> -. x = x)
5	4	intnan 755	. . . . . . 7 |- -. (w e. z /\ A.x(x = x <-> -. x = x))
6	5	nex 1456	. . . . . 6 |- -. E.w(w e. z /\ A.x(x = x <-> -. x = x))
7	6	nbn 791	. . . . 5 |- (-. y e. x <-> (y e. x <-> E.w(w e. z /\ A.x(x = x <-> -. x = x))))
8	7	albii 1346	. . . 4 |- (A.y -. y e. x <-> A.y(y e. x <-> E.w(w e. z /\ A.x(x = x <-> -. x = x))))
9	8	exbii 1398	. . 3 |- (E.xA.y -. y e. x <-> E.xA.y(y e. x <-> E.w(w e. z /\ A.x(x = x <-> -. x = x))))
10	1, 9	sylibr 217	. 2 |- (A.wE.xA.y(A.x(x = x <-> -. x = x) -> y = x) -> E.xA.y -. y e. x)
11		19.8a 1376	. . 3 |- (A.y(A.x(x = x <-> -. x = x) -> y = x) -> E.xA.y(A.x(x = x <-> -. x = x) -> y = x))
12	4	pm2.21i 93	. . 3 |- (A.x(x = x <-> -. x = x) -> y = x)
13	11, 12	mpg 1332	. 2 |- E.xA.y(A.x(x = x <-> -. x = x) -> y = x)
14	10, 13	mpg 1332	1 |- E.xA.y -. y e. x

Syntax hints:  -. wn 2   -> wi 3   <-> wb 163   /\ wa 240  A.wal 1296   = wceq 1298   e. wcel 1300  E.wex 1326

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7  ax-gen 1305  ax-4 1319  ax-5o 1321  ax-rep 3428

This theorem depends on definitions:  df-bi 164  df-an 242  df-ex 1327

Copyright terms: Public domain