English: Illustration for a proof of the Erdős–Anning theorem, that a non-collinear set of points in the plane with integer distances must be finite. Given three non-collinear points A, B, C in the set (here, the vertices of a 3-4-5 right triangle), the points whose distances to A and to B differ by an integer must lie on a system of hyperbolas and degenerate hyperbolas (blue), and symmetrically the points whose distances to B and to C differ by an integer must lie on another system of hyperbolas (red). Any point that has integer distance to all three of A, B, C must lie on one of the finitely many intersections of a blue and a red curve. Each branch of a hyperbola is labeled by the integer difference of distances that is invariant for the points on that branch.