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3 votes

Proposals for polymath projects

All trees are graceful, probably A graceful labelling of a (finite) tree with $n$ vertices is a bijection from $\{1,2,\ldots,n\}$ to the vertices of the tree such that each of the numbers in $\{1,2,\...
2 votes

A geometric interpretation of the fractional Fourier transform

For the record, to answer Q2, let me write down the Mehler kernel for the square root of the Fourier transform, $$K(x,y)=(2\pi)^{-1/2}\sqrt{1-i}\exp\left[{\tfrac{1}{2} i \left(x^2+y^2-2 \sqrt{2} x y\...
3 votes

Intuition behind Kleene's “second algebra” $\mathcal{K}_2$

There's a bit of explanation in my lecture notes on intuitionistic logic, in particular the section on function realizability. The idea is that you want to encode continuous partial functions $\mathbb{...
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