Theorem exists1 1996

Description: Two ways to express "only one thing exists." The left-hand side requires only one variable to express this. Both sides are false in set theory. (Contributed by NM, 5-Apr-2004.)

Assertion

Ref	Expression
exists1	|- ( E! x x = x <-> A. x x = y )

Distinct variable group:   x, y

Proof of Theorem exists1

Step	Hyp	Ref	Expression
1		df-eu 1903	. 2 |- ( E! x x = x <-> E. y A. x ( x = x <-> x = y ) )
2		equid 1589	. . . . . 6 |- x = x
3	2	tbt 236	. . . . 5 |- ( x = y <-> ( x = y <-> x = x ) )
4		bicom 128	. . . . 5 |- ( ( x = y <-> x = x ) <-> ( x = x <-> x = y ) )
5	3, 4	bitri 173	. . . 4 |- ( x = y <-> ( x = x <-> x = y ) )
6	5	albii 1359	. . 3 |- ( A. x x = y <-> A. x ( x = x <-> x = y ) )
7	6	exbii 1496	. 2 |- ( E. y A. x x = y <-> E. y A. x ( x = x <-> x = y ) )
8		hbae 1606	. . 3 |- ( A. x x = y -> A. y A. x x = y )
9	8	19.9h 1534	. 2 |- ( E. y A. x x = y <-> A. x x = y )
10	1, 7, 9	3bitr2i 197	1 |- ( E! x x = x <-> A. x x = y )

Syntax hints:   <-> wb 98   A.wal 1241   E.wex 1381   E!weu 1900

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-io 630  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-10 1396  ax-11 1397  ax-i12 1398  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427

This theorem depends on definitions:  df-bi 110  df-eu 1903

This theorem is referenced by:  exists2  1997