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 30607. 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  827  ecase2d  1043  efald  1583  necon1ai  2986  supgtoreq  9419  konigthlem  10528  indpi  10867  sqrmo  15280  2sqcoprm  27501  axtgupdim2  28642  ncoltgdim2  28736  ex-natded5.13  30619  bnj1204  35309  knoppndvlem10  36964  hashnexinj  42750  supxrgere  45914  supxrgelem  45918  supxrge  45919  iccdifprioo  46097  icccncfext  46466  stirlinglem5  46657  sge0repnf  46965  sge0split  46988  nnfoctbdjlem  47034  nabctnabc  47530