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Theorem 2eu7 1991
 Description: Two equivalent expressions for double existential uniqueness. (Contributed by NM, 19-Feb-2005.)
Assertion
Ref Expression
2eu7 ((∃!xyφ ∃!yxφ) ↔ ∃!x∃!y(xφ yφ))

Proof of Theorem 2eu7
StepHypRef Expression
1 hbe1 1381 . . . 4 (xφxxφ)
21hbeu 1918 . . 3 (∃!yxφx∃!yxφ)
32euan 1953 . 2 (∃!x(∃!yxφ yφ) ↔ (∃!yxφ ∃!xyφ))
4 ancom 253 . . . . 5 ((xφ yφ) ↔ (yφ xφ))
54eubii 1906 . . . 4 (∃!y(xφ yφ) ↔ ∃!y(yφ xφ))
6 hbe1 1381 . . . . 5 (yφyyφ)
76euan 1953 . . . 4 (∃!y(yφ xφ) ↔ (yφ ∃!yxφ))
8 ancom 253 . . . 4 ((yφ ∃!yxφ) ↔ (∃!yxφ yφ))
95, 7, 83bitri 195 . . 3 (∃!y(xφ yφ) ↔ (∃!yxφ yφ))
109eubii 1906 . 2 (∃!x∃!y(xφ yφ) ↔ ∃!x(∃!yxφ yφ))
11 ancom 253 . 2 ((∃!xyφ ∃!yxφ) ↔ (∃!yxφ ∃!xyφ))
123, 10, 113bitr4ri 202 1 ((∃!xyφ ∃!yxφ) ↔ ∃!x∃!y(xφ yφ))
 Colors of variables: wff set class Syntax hints:   ∧ wa 97   ↔ wb 98  ∃wex 1378  ∃!weu 1897 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 629  ax-5 1333  ax-7 1334  ax-gen 1335  ax-ie1 1379  ax-ie2 1380  ax-8 1392  ax-10 1393  ax-11 1394  ax-i12 1395  ax-bnd 1396  ax-4 1397  ax-17 1416  ax-i9 1420  ax-ial 1424  ax-i5r 1425 This theorem depends on definitions:  df-bi 110  df-tru 1245  df-nf 1347  df-sb 1643  df-eu 1900  df-mo 1901 This theorem is referenced by: (None)
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