A counterexample to Kusner's conjecture on equilateral sets

We disprove Kusner’s 1983 conjecture that every equilateral set in ${\mathrm{\ell }}_p^n$ with $2<p<\mathrm{\infty }$ has at most $n+1$ points: there exist $58$ points in ${\mathbb{R}}^{56}$ whose pairwise ${\mathrm{\ell }}_5$ distances are all equal, so the maximum equilateral-set size satisfies $e({\mathrm{\ell }}_5^{56})\ge 58>57$. This is the first equilateral set of more than $n+1$ points in ${\mathrm{\ell }}_p^n$ for any finite $p\ge 2$. The construction persists on an open interval of exponents around $5$; since Ge, Xu and Zhou recently proved the conjecture for $2\le p\le 4$, the infimum of exponents at which it fails lies in $[4,5)$. The configuration is the unique solution of an explicit polynomial system with rational coefficients in a rational box, established in exact arithmetic.