The circle of this construction is known as the circle of Thales. Further, Thales also said that:
- When two straight lines intersect one another the opposite angles are equal, and . . .
- That two triangles having two angles and one side that are respectively equal are themselves equal; and .
- that the sum of the angles in a triangle is equal to two right angles, and . . .
- That is a circle is bisected by it's diameter, and . . .
- that the angles at the base of an isoseles triangle are equal.