The two-distance sets in dimension four.

A finite set of distinct vectors $mathcal{X}$ in the $d$-dimensional Euclidean space $mathbb{R}^d$ is called a $2$-distance set, if the set of mutual distances between distinct elements of $mathcal{X}$ has cardinality exactly $2$. In this note we classify the $2$-distance sets in $mathbb{R}^4$ up to isometry with computer-aided methods.