Theorem notnotrd 134

Description: Deduction associated with notnotr 131 and notnotri 132. Double negation elimination rule. A translation of the natural deduction rule ¬ ¬ C , Γ⊢ ¬ ¬ 𝜓 ⇒ Γ⊢ 𝜓; see natded 30695. 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 131	. 2 ⊢ (¬ ¬ 𝜓 → 𝜓)
3	1, 2	syl 18	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  829  ecase2d  1045  efald  1588  necon1ai  2991  supgtoreq  9431  konigthlem  10553  indpi  10892  sqrmo  15302  2sqcoprm  27565  axtgupdim2  28706  ncoltgdim2  28800  ex-natded5.13  30707  bnj1204  35345  knoppndvlem10  37033  hashnexinj  42820  supxrgere  45976  supxrgelem  45980  supxrge  45981  iccdifprioo  46159  icccncfext  46528  stirlinglem5  46719  sge0repnf  47027  sge0split  47050  nnfoctbdjlem  47096  nabctnabc  47592