The tomahawk is a "tool" in geometry consisting of a semicircle and two line segments. The basic shape is constructible with compass and straightedge. It is possible to trisect an angle with the tomahawk. This does not contradict the usual theorem stating that an arbitrary angle cannot be trisected by compass and unmarked straightedge alone, as translating the constructed tomahawk into the required position is not a Euclidean construction.