Mitch Harris
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 Feb 22 awarded Nice Answer Oct 8 awarded Constituent Oct 8 awarded Caucus Jun 25 awarded Yearling Nov 15 awarded Popular Question Jul 30 comment Most striking applications of category theory? This would be an excellent example if only it were followed up with some detail and references. Jan 31 comment Can a polynomial size CFG describe the finite language \{$w \pi(w)$ : $\pi(w)$ is fixed string permutation, $|w|=n$ is fixed\} over alphabet \{0,1\}? polynomial size in what? $n$? And is $n$ encoded in binary? It seems the CNF grammar is what you're seeking given the permutation $\pi$ and the length of the strings $n$. Jan 27 comment Nontrivial circular arguments? Every circular proof is also a proof of equivalence. That is, the unsatisfying circular proof, using an assumption that ends up depending on the thing to be proved, is also a proof the assumption is equivalent to the conclusion (they both imply each other). The hard part is to extract from the disappointment the bidirection or circle of implication. Jan 14 answered Equational logic Jan 11 answered Is finitism an extreme form of constructivism? Jan 5 comment Computer Science for Mathematicians Computer architecture (a la Patterson and Hennessey) as interesting and useful and having mathematical underpinnings and relevant to understanding motivations for TCS as it is, is in no way TCS and is not mathematics. Jan 5 comment Computer Science for Mathematicians @Igor - I was about to say the same thing, but it certainly is a text about mathematics that is inspired by thinking about writing programs...well, those programs that Don Knuth was thinking about in 1960. Jan 5 comment Computer Science for Mathematicians Intro to Automata Theory, Languages, and Computation, Hopcroft, Ullman, Motwani infolab.stanford.edu/~ullman/ialc.html is a good alternative. Jan 4 comment Collatz conjecture for numbers of th form $2^n +1$ If you plot the numbers, some interesting patterns emerge (mostly increasing but with scattered outliers, and longer and longer incremental sequences). A very different pattern from the usual Collatz 'number of steps' function A006577. Jan 4 comment Collatz conjecture for numbers of th form $2^n +1$ The sequence has been submitted to OEIS (not yet approved) with links here. Jan 4 answered Algorithm for summing certain sums involving the floor function Jan 3 awarded Commentator Jan 3 comment Unpopular “elementary” theorems/identities to impress an audience of mathematicians. +1 simply for pointing out Marden's theorem. Dec 30 comment The Mystic Rose The function given there is for equally spaced points on a circle, and links there go to explanations and formulas. One link on that OEIS page is to: oeis.org/A005732 for general position points on a circle, and gives the formula C(n+3,6)+C(n+1,5)+C(n,5) surely equivalent to a formula at your relevant blog posting. Dec 11 comment Is pattern recognition NP-complete? 'Pattern Recognition' seems too general a name for this problem. It sounds more like interpolation.