I've taken courses in formal logic at multiple levels. All that notation is familiar and the explanation seems correct if vacuous.
--- Frank C. Wimberly 140 Calle Ojo Feliz, Santa Fe, NM 87505 505 670-9918 Santa Fe, NM On Tue, Dec 27, 2022, 3:19 AM David Eric Smith <[email protected]> wrote: > Interesting. Lack of global awareness duly noted. > > But also, can you check me on this?: > > > On Dec 26, 2022, at 7:21 PM, glen <[email protected]> wrote: > > > > This exchange was interesting. I've never seen ⊃° used. > > > > ⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄ > > me: What is the difference between ⊃ and ⊢. > > > > gpt: The symbol "⊃" is the logical symbol for "implies." It is used to > form conditional statements in which the formula on the right is true only > if the formula on the left is true. For example, the formula "A ⊃ B" can be > read as "A implies B," and it means that if A is true, then B must also be > true. > > Am I somehow blanking on ordinary sign-flips, or mistaking left and right? > > Seems B Is true _if_ A is true. B is false _only if_ A is false == If A > is true, then B must also be true. > > Given that English is not ensured to have any global internal logical > consistency, one can see making sentences that don’t close internally. But > in areas where English is capable of being used with internal consistency, > I am surprised to see an “only if” transposed with an “if” everywhere. Did > I completely misunderstand what “implies” means? > > > On all this I feel completely exposed: I thought I remembered from Quine’s > little book on propositional calculus that “implies” isn’t even an > elementary operator; only enters in a context like modus ponens for > proofs. In first-order logic one was supposed to write expressions such as > “B or not(A)” to mean “if A then B”. And there was some other symbol (even > simpler than the entails) for that conditional. > > Eric > > > > -. --- - / ...- .- .-.. .. -.. / -- --- .-. ... . / -.-. --- -.. . > FRIAM Applied Complexity Group listserv > Fridays 9a-12p Friday St. Johns Cafe / Thursdays 9a-12p Zoom > https://bit.ly/virtualfriam > to (un)subscribe http://redfish.com/mailman/listinfo/friam_redfish.com > FRIAM-COMIC http://friam-comic.blogspot.com/ > archives: 5/2017 thru present > https://redfish.com/pipermail/friam_redfish.com/ > 1/2003 thru 6/2021 http://friam.383.s1.nabble.com/ >
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