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 Apr 6 awarded Yearling Apr 3 comment Is the two variable fragment of arithmetic, i.e., theory of ($\mathbb{N}, + ,\times$), decidable? Sorry, I should have asked "Is every sentence equivalent to a boolean combination of 2-quantifier formulas in prenex form?" Also, It would be helpful if you said what you mean by "the two variable fragment of arithmetic". Apr 3 comment Is the two variable fragment of arithmetic, i.e., theory of ($\mathbb{N}, + ,\times$), decidable? In "two-variable arithmetic" does every sentence have an equivalent prenex form consisting of an $x$-quantifier and a $y$-quantifier (in some order) followed by an open formula? Jan 21 awarded Good Answer Dec 16 comment How Symmetric is Diophantine Approximation using Fractions with Square Denominators? These can't be all of the best approximations, because they are all less than the Liouville number. Dec 14 comment A question regarding a fragment of Robinson Arithmetic In your language you can say that every element is even or odd. This is true in the non-negative integers under addition but false for the set of polynomials with non-negative leading coefficients (under addition, with successor defined in the obvious way.) May 18 awarded Nice Question Apr 6 awarded Yearling Apr 3 revised divisible by all standard prime numbers deleted 2 characters in body Apr 2 revised divisible by all standard prime numbers added 16 characters in body Apr 2 revised divisible by all standard prime numbers deleted 32 characters in body Apr 2 revised divisible by all standard prime numbers added 32 characters in body Apr 2 answered divisible by all standard prime numbers Jan 22 awarded Enlightened Jan 22 awarded Nice Answer Sep 10 awarded Enlightened Aug 27 comment Algorithm for determining when polynomial iteration is bounded? @Per: Thank you for the reference to the result on IFS undecidability. Alas, I don't see how to the IFS result here. However the second point, about the map $x\to x-1/x$ seems really interesting. Do you have a reference? Aug 26 asked Algorithm for determining when polynomial iteration is bounded? Jul 2 awarded Curious Jun 14 awarded Enlightened