Lines {diagonal} can go from one vertex to non-adjacent vertex. Tetrahedron and Csaszar polyhedron have no diagonals.
If two lines are perpendicular {perpendicular lines}, line slopes are negative reciprocals: m2 = -1 / m1, where m1 and m2 are slopes.
Regular pyramid has apex and lateral face, which has median {slant height, pyramid} through apex.
Space can have non-intersecting, non-parallel lines {skew line}.
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Date Modified: 2022.0225