Declared in <mp-units/framework/customization_points.h>
template<typename T>
requires (!detail::has_ambiguous_order<T>)
constexpr std::size_t tensor_order<T> = detail::has_matrix_indexing<T> ? std::size_t{2}
: detail::has_vector_indexing<T> ? std::size_t{1}
: std::size_t{0};