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Theorem 2exnexn 1580
Description: Theorem *11.51 in [WhiteheadRussell] p. 164. (Contributed by Andrew Salmon, 24-May-2011.) (Proof shortened by Wolf Lammen, 25-Sep-2014.)
Assertion
Ref Expression
2exnexn (xyφ ↔ ¬ xy ¬ φ)

Proof of Theorem 2exnexn
StepHypRef Expression
1 alexn 1579 . 2 (xy ¬ φ ↔ ¬ xyφ)
21con2bii 322 1 (xyφ ↔ ¬ xy ¬ φ)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 176  wal 1540  wex 1541
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1546  ax-5 1557
This theorem depends on definitions:  df-bi 177  df-ex 1542
This theorem is referenced by: (None)
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