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Theorem mon 1926
Description: There is at most one of something which does not exist. (Contributed by Jim Kingdon, 5-Jul-2018.)
Assertion
Ref Expression
mon xφ∃*xφ)

Proof of Theorem mon
StepHypRef Expression
1 ax-in2 545 . 2 xφ → (xφ∃!xφ))
2 df-mo 1901 . 2 (∃*xφ ↔ (xφ∃!xφ))
31, 2sylibr 137 1 xφ∃*xφ)
Colors of variables: wff set class
Syntax hints:  ¬ wn 3  wi 4  wex 1378  ∃!weu 1897  ∃*wmo 1898
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-in2 545
This theorem depends on definitions:  df-bi 110  df-mo 1901
This theorem is referenced by:  moexexdc  1981
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