Theorem notnotrd 133

Description: Deduction associated with notnotr 130 and notnotri 131. Double negation elimination rule. A translation of the natural deduction rule ¬ ¬ C , Γ⊢ ¬ ¬ 𝜓 ⇒ Γ⊢ 𝜓; see natded 29920. This is Definition NNC in [Pfenning] p. 17. This rule is valid in classical logic (our logic), but not in intuitionistic logic. (Contributed by DAW, 8-Feb-2017.)

Hypothesis

Ref	Expression
notnotrd.1	⊢ (𝜑 → ¬ ¬ 𝜓)

Assertion

Ref	Expression
notnotrd	⊢ (𝜑 → 𝜓)

Proof of Theorem notnotrd

Step	Hyp	Ref	Expression
1		notnotrd.1	. 2 ⊢ (𝜑 → ¬ ¬ 𝜓)
2		notnotr 130	. 2 ⊢ (¬ ¬ 𝜓 → 𝜓)
3	1, 2	syl 17	1 ⊢ (𝜑 → 𝜓)

Syntax hints:  ¬ wn 3   → wi 4

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem is referenced by:  condan  815  ecase2d  1027  efald  1561  necon1ai  2967  supgtoreq  9468  konigthlem  10566  indpi  10905  sqrmo  15203  2sqcoprm  27171  axtgupdim2  27986  ncoltgdim2  28080  ex-natded5.13  29932  bnj1204  34318  knoppndvlem10  35701  supxrgere  44343  supxrgelem  44347  supxrge  44348  iccdifprioo  44529  icccncfext  44903  stirlinglem5  45094  sge0repnf  45402  sge0split  45425  nnfoctbdjlem  45471  nabctnabc  45941