An explicit counterexample to the Hinrichs--Vybiral conjecture

Jan Vybiral

Conjecture~2 of Hinrichs and Vybíral asserts that every continuous, nonnegative, positive definite function $f$ on ${\mathbb{R}}^d$, normalized by $f(0)=1$, satisfies $[f(x_j-x_k)]_{j,k=1}^n…