For non-empty subsets A,B⊂Z define A+B={a+b:a∈A,b∈B},A−B={a−b:a∈A,b∈B}.In the sequel we work with non-empty finite subsets of Z.Prove that we can cover B by at most ∣A∣∣A+B∣ translates of A−A, i.e. there exists X⊂Z with ∣X∣≤∣A∣∣A+B∣ such that B⊆∪x∈X(x+(A−A))=X+A−A.