arc. a tournament. T then models a round robin tournament. the verices of T and the teams in the round robin tournament and (u,v) is an arc in T if team u defat team u (Ties are not permitted.) Recall that two digraphs D and D' are isomorphic, written as D D', If there exists a bijectvie function ....... such that(u,v) ... If and only if ..... such a function is called an isomorphism there is only one tournament of order 1 and only one tournament of order 2(up to isomorphism)