Sum of angles of a triangle The relation between angular defect and the triangle's area was first proven by Johann Heinrich Lambert. One can easily see how hyperbolic geometry breaks Playfair's axiom, Proclus' axiom (the parallelism, defined as non-intersection, is intransitive in an hyperbolic plane), the equidistance postulate (the points on one side of, and equidistant from, a given line do not form a line), and Pythagoras' theorem. A circle cannot have arbitrarily small curvature, so the three points property also fails. The sum of the angles can be arbitrarily small (but positive). For an ideal triangle, a generalization of hyperbolic triangles, this sum is equal
Proofs of Fermat's theorem on sums of two squares of which is a sum of two squares, is itself a sum of two squares." 2. "If a number which is a sum of two squares is divisible by a prime which is a sum of two squares, then the quotient is a sum of two squares." (This is Euler's first Proposition). 3. "If a number which can be written as a sum of two squares is divisible by a number which is not a sum of two squares, then the quotient has a factor which is not a sum of two squares." (This is Euler's second Proposition). 4. "If