Peter Smith
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 1d comment Algebra and Logic And what's the question? "Characterize ..." "Verify ...", "Prove ..." are imperatives -- and we aren't here to be instructed to do your homework for you. 1d revised Reconstructing the conditional's truth table from natural deduction added 46 characters in body 1d answered Reconstructing the conditional's truth table from natural deduction Apr6 revised categorical interpretation of quantification edited body Apr5 comment Let $\tau$ be a closed tableau. Prove that $\tau$ is not satisfiable. It isn't good form here, when someone has taken the trouble to answer a question, to change it to something so different that the answer no long applies. Your revised question suggests you haven't worked through the suggested reading of the answer to your original question that you will find if many textbooks. Apr5 answered Let $\tau$ be a closed tableau. Prove that $\tau$ is not satisfiable. Apr2 comment Is there a way of making the notion of “stronger theorem” precise? @RobArthan I didn't give an analysis -- I was just trying to get out of the way that claim that all theorems in a formal system imply each other, which was supposed to show that that talk about one theorem being stronger than another doesn't even make sense. Apr2 revised Is there a way of making the notion of “stronger theorem” precise? added 35 characters in body Apr2 answered Is there a way of making the notion of “stronger theorem” precise? Mar26 comment Examples of functors that preserves products but not equalizers, and vice versa. Thanks! Those are just the kind of neat "entry-level" examples I was hoping for. Mar26 accepted Examples of functors that preserves products but not equalizers, and vice versa. Mar25 asked Examples of functors that preserves products but not equalizers, and vice versa. Mar25 comment Are the Godel's incompleteness theorems valid for both classical and intuitionistic logic? Do "people sometimes say that infinities are the troublemakers" with respect to Gödelian incompleteness? Really? Which infinities?? Mar22 answered Predicate Logic Practice Mar22 revised Predicate Calculus Challenge Practice Question added 679 characters in body Mar22 answered Predicate Calculus Challenge Practice Question Mar21 comment difference between functors and predicates The comment should have read: That seems to confuse functors (function symbols) with functions, and predicates with relations. It is relations which "accept objects", while predicates are symbols which get concatenated with terms to form wffs: predicates have relations as their semantic values. Likewise functors are symbolic entities, certainly in the usage of the quoted notes, which have functions as their semantic values Mar16 comment Does the square or the circle have the greater perimeter? A surprisingly hard problem for high schoolers I find it interesting, indeed odd, that fewer have upvoted this entirely natural proof than the "3.4.5" trick. This proof almost writes itself when you think (1) "Hey, I'll surely need to compare a diameter of the circle with an edge" (2) "The obvious diameter to look at is the one through E" (3) "And if I'm going to comparing straight lines here, surely looking for similar triangles has to be the way to go ..."". Mar13 revised What are the uses of cross-theoretic identifications within mathematics? added 7 characters in body Mar13 answered What are the uses of cross-theoretic identifications within mathematics?