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Theorem modal-5 1749
Description: The analog in our predicate calculus of axiom 5 of modal logic S5. (Contributed by NM, 5-Oct-2005.)
Assertion
Ref Expression
modal-5  |-  ( -. 
A. x  -.  ph  ->  A. x  -.  A. x  -.  ph )

Proof of Theorem modal-5
StepHypRef Expression
1 hbn1 1746 1  |-  ( -. 
A. x  -.  ph  ->  A. x  -.  A. x  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4   A.wal 1550
This theorem was proved from axioms:  ax-6 1745
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