std::linalg::possibly-multipliable

namespace std::linalg {
  template<in-matrix InMat, in-vector InVec, in-vector OutVec>
  constexpr bool possibly-multipliable()
  {
    return compatible-static-extents<OutVec, InMat>(0, 0) &&
           compatible-static-extents<InMat, InVec>(1, 0);
  } // (1)

  template<in-vector InVec, in-matrix InMat, in-vector OutVec>
  constexpr bool possibly-multipliable()
  {
    return compatible-static-extents<OutVec, InMat>(0, 1) &&
           compatible-static-extents<InMat, InVec>(0, 0);
  } // (2)

  template<in-matrix InMat1, in-matrix InMat2, in-matrix OutMat>
  constexpr bool possibly-multipliable()
  {
    return compatible-static-extents<OutMat, InMat1>(0, 0) &&
           compatible-static-extents<OutMat, InMat2>(1, 1) &&
           compatible-static-extents<InMat1, InMat2>(1, 0);
  } // (3)
}