Theorem dftest 855

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

Step	Hyp	Ref	Expression
1		df-dc 776	1 ⊢ (DECID ¬ 𝜑 ↔ (¬ 𝜑 ∨ ¬ ¬ 𝜑))

Syntax hints:  ¬ wn 3   ↔ wb 103   ∨ wo 661  DECID wdc 775

This theorem depends on definitions:  df-dc 776

This theorem is referenced by: (None)