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Theorem euequ1 1992
 Description: Equality has existential uniqueness. (Contributed by Stefan Allan, 4-Dec-2008.)
Assertion
Ref Expression
euequ1 ∃!x x = y
Distinct variable group:   x,y

Proof of Theorem euequ1
Dummy variable z is distinct from all other variables.
StepHypRef Expression
1 a9e 1583 . 2 x x = y
2 equtr2 1594 . . 3 ((x = y z = y) → x = z)
32gen2 1336 . 2 xz((x = y z = y) → x = z)
4 equequ1 1595 . . 3 (x = z → (x = yz = y))
54eu4 1959 . 2 (∃!x x = y ↔ (x x = y xz((x = y z = y) → x = z)))
61, 3, 5mpbir2an 848 1 ∃!x x = y
 Colors of variables: wff set class Syntax hints:   → wi 4   ∧ wa 97  ∀wal 1240  ∃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-nf 1347  df-sb 1643  df-eu 1900  df-mo 1901 This theorem is referenced by:  copsexg  3972  oprabid  5480
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