Theorem iotanul 5256

Description: Theorem 8.22 in [Quine] p. 57. This theorem is the result if there isn't exactly one x that satisfies ph. (Contributed by Andrew Salmon, 11-Jul-2011.)

Assertion

Ref	Expression
iotanul	|- ( -. E! x ph -> ( iota x ph ) = (/) )

Proof of Theorem iotanul

Dummy variable z is distinct from all other variables.

Step	Hyp	Ref	Expression
1		df-eu 2058	. . 3 |- ( E! x ph <-> E. z A. x ( ph <-> x = z ) )
2		dfiota2 5242	. . . 4 |- ( iota x ph ) = U. { z | A. x ( ph <-> x = z ) }
3		alnex 1523	. . . . . . 7 |- ( A. z -. A. x ( ph <-> x = z ) <-> -. E. z A. x ( ph <-> x = z ) )
4		ax-in2 616	. . . . . . . . . 10 |- ( -. A. x ( ph <-> x = z ) -> ( A. x ( ph <-> x = z ) -> -. z = z ) )
5	4	alimi 1479	. . . . . . . . 9 |- ( A. z -. A. x ( ph <-> x = z ) -> A. z ( A. x ( ph <-> x = z ) -> -. z = z ) )
6		ss2ab 3265	. . . . . . . . 9 |- ( { z | A. x ( ph <-> x = z ) } C_ { z | -. z = z } <-> A. z ( A. x ( ph <-> x = z ) -> -. z = z ) )
7	5, 6	sylibr 134	. . . . . . . 8 |- ( A. z -. A. x ( ph <-> x = z ) -> { z | A. x ( ph <-> x = z ) } C_ { z | -. z = z } )
8		dfnul2 3466	. . . . . . . 8 |- (/) = { z | -. z = z }
9	7, 8	sseqtrrdi 3246	. . . . . . 7 |- ( A. z -. A. x ( ph <-> x = z ) -> { z | A. x ( ph <-> x = z ) } C_ (/) )
10	3, 9	sylbir 135	. . . . . 6 |- ( -. E. z A. x ( ph <-> x = z ) -> { z | A. x ( ph <-> x = z ) } C_ (/) )
11	10	unissd 3880	. . . . 5 |- ( -. E. z A. x ( ph <-> x = z ) -> U. { z | A. x ( ph <-> x = z ) } C_ U. (/) )
12		uni0 3883	. . . . 5 |- U. (/) = (/)
13	11, 12	sseqtrdi 3245	. . . 4 |- ( -. E. z A. x ( ph <-> x = z ) -> U. { z | A. x ( ph <-> x = z ) } C_ (/) )
14	2, 13	eqsstrid 3243	. . 3 |- ( -. E. z A. x ( ph <-> x = z ) -> ( iota x ph ) C_ (/) )
15	1, 14	sylnbi 680	. 2 |- ( -. E! x ph -> ( iota x ph ) C_ (/) )
16		ss0 3505	. 2 |- ( ( iota x ph ) C_ (/) -> ( iota x ph ) = (/) )
17	15, 16	syl 14	1 |- ( -. E! x ph -> ( iota x ph ) = (/) )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 105   A.wal 1371   = wceq 1373   E.wex 1516   E!weu 2055   {cab 2192   C_ wss 3170   (/)c0 3464   U.cuni 3856   iotacio 5239

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 615  ax-in2 616  ax-io 711  ax-5 1471  ax-7 1472  ax-gen 1473  ax-ie1 1517  ax-ie2 1518  ax-8 1528  ax-10 1529  ax-11 1530  ax-i12 1531  ax-bndl 1533  ax-4 1534  ax-17 1550  ax-i9 1554  ax-ial 1558  ax-i5r 1559  ax-ext 2188

This theorem depends on definitions:  df-bi 117  df-tru 1376  df-fal 1379  df-nf 1485  df-sb 1787  df-eu 2058  df-clab 2193  df-cleq 2199  df-clel 2202  df-nfc 2338  df-ral 2490  df-rex 2491  df-v 2775  df-dif 3172  df-in 3176  df-ss 3183  df-nul 3465  df-sn 3644  df-uni 3857  df-iota 5241

This theorem is referenced by:  tz6.12-2  5580  0fv  5625  riotaund  5947  0g0  13283