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Mirrors > Home > ILE Home > Th. List > dftest | GIF version |
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.) |
Ref | Expression |
---|---|
dftest | ⊢ (DECID ¬ 𝜑 ↔ (¬ 𝜑 ∨ ¬ ¬ 𝜑)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-dc 743 | 1 ⊢ (DECID ¬ 𝜑 ↔ (¬ 𝜑 ∨ ¬ ¬ 𝜑)) |
Colors of variables: wff set class |
Syntax hints: ¬ wn 3 ↔ wb 98 ∨ wo 629 DECID wdc 742 |
This theorem depends on definitions: df-dc 743 |
This theorem is referenced by: (None) |
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