x1 is aligned diagonally along/between nonadjacent vertices x2 as in polytope x3; x1 is a diagonal line segment/linear manifold of lower dimension as viewed in frame of reference x3; x1 is crooked (one sense), skew (one sense, see notes), off-kilter (one sense), away from center/off-center, non-orthogonal/not perpendicular nor parallel, at an angle, perhaps non-vertical and non-horizontal, diagonal to x2 in figure/coordinate system x3.