Mathematical contradiction

The Hand is one of several symbols sometimes used to designate the conclusion of a mathematical proof by contradiction. In this setting, it is usually drawn horizontally, with little or no adornment, or some minor variant thereof. While less compact than some of the alternatives (such as the blitz or crosshatch), The Hand has the advantage of being visually suggestive of the core concept of this method of reasoning: The conflicting conclusions are represented by the two arrows, and in order to avoid an impasse, one set of assumptions must give way.

The method of proof by contradiction has also been used to show that for any non-degenerate right triangle, the length of the hypotenuse is less than the sum of the lengths of the two remaining sides. The proof relies on the Pythagorean theorem.