template<in-matrix InMat1, in-matrix InMat2, out-matrix OutMat>
void matrix_product(InMat1 A, InMat2 B, OutMat C);
template<class ExecutionPolicy, in-matrix InMat1, in-matrix InMat2, out-matrix OutMat>
void matrix_product(ExecutionPolicy&& exec, InMat1 A, InMat2 B, OutMat C);
template<in-matrix InMat1, in-matrix InMat2, in-matrix InMat3, out-matrix OutMat>
void matrix_product(InMat1 A, InMat2 B, InMat3 E, OutMat C);
template<class ExecutionPolicy,
in-matrix InMat1, in-matrix InMat2, in-matrix InMat3, out-matrix OutMat>
void matrix_product(ExecutionPolicy&& exec, InMat1 A, InMat2 B, InMat3 E, OutMat C);