Ring of the Fisherman Ring of the Fisherman The Ring of the Fisherman (Latin: "Annulus Piscatoris"; Italian: "Anello Piscatorio"), also known as the Piscatory Ring, is an official part of the regalia worn by the Pope, who is head of the Catholic Church and successor of Saint Peter who was a fisherman by trade. It used to feature a bas-relief of Peter fishing from a boat, a symbolism derived from the tradition that the apostles were "fishers of men" (Mark 1:17). The Fisherman's Ring is a signet used until 1842 to seal official documents signed by the Pope. A letter written by Pope Clement
Uniquely colorable graph cubic graph is uniquely 3-edge-colorable, it must have exactly three Hamiltonian cycles, formed by the edges with two of its three colors, but some cubic graphs with only three Hamiltonian cycles are not uniquely 3-edge-colorable . Every simple planar cubic graph that is uniquely 3-edge-colorable contains a triangle , but observed that the generalized Petersen graph "G"(9,2) is non-planar, triangle-free, and uniquely 3-edge-colorable. For many years it was the only known such graph, and it had been conjectured to be the only such graph (see and ) but now infinitely many triangle-free non-planar cubic uniquely 3-edge-colorable graphs are known .