Semidefinite code bounds based on quadruple distances

Dion C. Gijswijt, Hans D. Mittelmann, Alexander Schrijver

Let $A(n,d)$ be the maximum number of $0,1$ words of length $n$, any two having Hamming distance at least $d$. We prove $A(20,8)=256$, which implies that the quadruply shortened Go…