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Theorem notal 25094
Description: It's false that  ph always holds iff  -.  ph eventually holds. (Contributed by FL, 20-Mar-2011.)
Assertion
Ref Expression
notal  |-  ( -. 
[.] ph  <->  <>  -.  ph )

Proof of Theorem notal
StepHypRef Expression
1 boxeq 25090 . . 3  |-  ( [.] ph 
<->  -.  <>  -.  ph )
21bicomi 193 . 2  |-  ( -.  <> 
-.  ph  <->  [.] ph )
32con1bii 321 1  |-  ( -. 
[.] ph  <->  <>  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    <-> wb 176   [.]wbox 25073   <>wdia 25074
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-ltl1 25077  ax-lmp 25081
This theorem depends on definitions:  df-bi 177  df-dia 25083
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