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Mirrors > Home > MPE Home > Th. List > notnot | Structured version Visualization version GIF version |
Description: Double negation introduction. Converse of notnotr 125 and one implication of notnotb 304. Theorem *2.12 of [WhiteheadRussell] p. 101. This was the sixth axiom of Frege, specifically Proposition 41 of [Frege1879] p. 47. (Contributed by NM, 28-Dec-1992.) (Proof shortened by Wolf Lammen, 2-Mar-2013.) |
Ref | Expression |
---|---|
notnot | ⊢ (𝜑 → ¬ ¬ 𝜑) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | id 22 | . 2 ⊢ (¬ 𝜑 → ¬ 𝜑) | |
2 | 1 | con2i 134 | 1 ⊢ (𝜑 → ¬ ¬ 𝜑) |
Colors of variables: wff setvar class |
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: notnoti 137 notnotd 138 con1d 139 con4iOLD 145 notnotb 304 biortn 421 pm2.13 434 nfntOLDOLD 1783 necon2ad 2809 necon4ad 2813 necon4ai 2825 eueq2 3380 ifnot 4133 knoppndvlem10 32512 wl-orel12 33294 cnfn1dd 33894 cnfn2dd 33895 axfrege41 38138 vk15.4j 38734 zfregs2VD 39076 vk15.4jVD 39150 con3ALTVD 39152 stoweidlem39 40256 |
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