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 30496. 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  818  ecase2d  1032  efald  1563  necon1ai  2960  supgtoreq  9388  konigthlem  10493  indpi  10832  sqrmo  15188  2sqcoprm  27419  axtgupdim2  28561  ncoltgdim2  28655  ex-natded5.13  30508  bnj1204  35194  knoppndvlem10  36749  hashnexinj  42527  supxrgere  45721  supxrgelem  45725  supxrge  45726  iccdifprioo  45905  icccncfext  46274  stirlinglem5  46465  sge0repnf  46773  sge0split  46796  nnfoctbdjlem  46842  nabctnabc  47320