bool operator==(const Line_E2<NT>& L) const { return (this == &L) || (are_dependent(_a, _b, _c, L._a, L._b, L._c) && inner_product(_a, _b, _c, L._a, L._b, L._c) > 0); }
//! Test if items (corresponding to vectors in matrix) in list are independent bool are_independent(const list_type& list) const { return !are_dependent(list); }