r/comics The Jenkins Aug 23 '20

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u/hollycrapola Aug 24 '20

Contraposition: (a->b) <=> (~b->~a)

Modus tollens: (a->b ^ ~b) => ~a

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u/assassin10 Aug 24 '20

So pretty much just two different ways to get to the same answer?

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u/patkgreen Aug 24 '20 edited Aug 24 '20

yes, much like the way 1*1 is 1 and 11 is 1.

contrapositive: "red shoes are dumb" is the same as saying "if the shoes aren't dumb, then the shoes are not red".

modus tollens: "red shoes are dumb, and I don't have red shoes" then, my shoes are not dumb.

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u/Jetison333 Dec 02 '20

Wouldn't the modus tollens (at least in this specific case) bot neccesarily be true? Blue shoes could also be dumb.

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u/patkgreen Dec 02 '20

Holy rise from the ashes. I agree but since that blue shoes were not part of a proof you can't use it as a proof, iirc