Exercise 11

Euclid describes a plane as “a surface which lies evenly with the straight lines on itself”. Commentators such as Heron have interpreted this to mean, “(A plane surface is) such that, if a straight line pass through two points on it, the line coincides wholly with it at every spot, all ways”. (Translations from , pp. 171-172.) Do planes, as described in this section, have that property? Does this description adequately define planes?