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https://mathoverflow.net/questions/508601/fixed-point-free-shrinking-bijection co.combinatorics - Fixed-point free shrinking bijection - MathOverflow Let $J\subseteq {\cal P}(\omega)$ be the collection of infinite subsets whose complement is also infinite. Is there a fixed-point free bijection $\varphi:J\to... co combinatorics fixed point free shrinking bijection mathoverflow https://mathoverflow.net/questions/21003/polynomial-bijection-from-mathbb-q-times-mathbb-q-to-mathbb-q nt.number theory - Polynomial bijection from $\mathbb Q\times\mathbb Q$ to $\mathbb Q$? -... Is there any polynomial $f(x,y)\in{\mathbb Q}[x,y]{}$ such that $f\colon\mathbb{Q}\times\mathbb{Q} \rightarrow\mathbb{Q}$ is a bijection? nt number theory polynomial bijection mathbb q https://mathoverflow.net/questions/117390/polynomial-bijection-from-zxz-to-z nt.number theory - Polynomial bijection from ZxZ to Z? - MathOverflow It is known that the polynomial $f(n,m)=\frac{1}{2}(n+m)(n+m+1)+m$ defines bijection $\mathbb{N}\times\mathbb{N}\to\mathbb{N}$ (Put pairs of $\mathbb{N}$ into... nt number theory polynomial bijection z mathoverflow