ABSTRACT
The list of axioms will now be expanded to include the familiar ideas about angles. An apparently trivial fact that each line separates the plane into two “sides” or “half planes” will also be introduced, which is the basis for further properties of angles. First, we introduce the concept of angles and their measure. At this point in our development, we discontinue the consistent use of arrow symbols and bars for lines, rays, and segments. The convention of letting the identity of the objects of the discussion be deŠned by context will be followed from now on, except when greater clariŠcation is desired.
