The basic notions

The notions, at least the mathematical, are like the forms of matter, which are split in molecules, these in atoms, these in elementary particles etc. In geometry the reduction to simpler and more elementary notions comes eventually to the so called undefined terms. These are notions, simple and familiar from our experience, for which it is difficult to find even simpler ones, with which to describe them ([24]). Such notions in geometry are the point, the plane, the space, the line, the notion of the point between two other points and the notion of equality of two shapes.