  “A point is that which has no part. A line is breadthless length.  The extremities of a line are points. […] A surface is that which has length and breadth only. The extremities of a surface are lines. […] A boundary is that which is an extremity of anything.” [Euclid, Elements, Bk I, Dfs 1–3, 5–6, 13 (1908: p. 153)]