In a round-robin tournament, every two distinct players play against each other just once. For a round-robin tournament with no tied games, a record of who beat whom can be described with a tournament digraph, where the vertices correspond to players and there is an edge (x -> y) if and only if x beat y in their game. A ranking is a path that includes all the players. So, in a ranking, each player won the game against the next lowest ranked player but may very well have lost their games against much lower ranked players - whoever does the ranking may have a lot of room to play favorites.
(a) Give an example of a tournament digraph with more than one ranking: Include a visualization of your digraph by embedding a picture of a hand-drawn digraph or by using some application to draw the graph.
(b) Prove that if a tournament digraph is a DAG, then it has at most one ranking.