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 28668. 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  814  ecase2d  1026  efald  1560  necon1ai  2970  supgtoreq  9159  konigthlem  10255  indpi  10594  sqrmo  14891  2sqcoprm  26488  axtgupdim2  26736  ncoltgdim2  26830  ex-natded5.13  28680  bnj1204  32892  knoppndvlem10  34628  supxrgere  42762  supxrgelem  42766  supxrge  42767  iccdifprioo  42944  icccncfext  43318  stirlinglem5  43509  sge0repnf  43814  sge0split  43837  nnfoctbdjlem  43883  nabctnabc  44313