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Theorem dftest 821
Description: A proposition is testable iff its negative or double-negative is true. See Chapter 2 [Moschovakis] p. 2.

Our notation for testability is DECID ¬ before the formula in question. For example, DECID ¬ x = y corresponds to "x = y is testable". (Contributed by David A. Wheeler, 13-Aug-2018.)

Assertion
Ref Expression
dftest (DECID ¬ φ ↔ (¬ φ ¬ ¬ φ))

Proof of Theorem dftest
StepHypRef Expression
1 df-dc 742 1 (DECID ¬ φ ↔ (¬ φ ¬ ¬ φ))
Colors of variables: wff set class
Syntax hints:  ¬ wn 3  wb 98   wo 628  DECID wdc 741
This theorem depends on definitions:  df-dc 742
This theorem is referenced by: (None)
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