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 The deletion of any vertex from a minimal imperfect graph leaves a uniquely colorable subgraph. A uniquely edge-colorable graph is a "k"-edge-chromatic graph that has only one possible (proper) "k"-edge-coloring up to permutation of the colors. The only uniquely 2-edge-colorable graphs are the paths and the cycles. For any "k", the stars "K" are the only uniquely "k"-edge-colorable graphs. Moreover, conjectured and proved that, when "k" ≥ 4, they are also the only members in this family. However, there exist uniquely 3-edge-colorable graphs that do not fit into this classification, such as the graph of the triangular pyramid. If a