This is showing a way of constructing a tournament graph. It's not necessarily the best way. The graph has two brackets; the normal bracket and a losers bracket, effectively giving everyone in the tournament (except one!) the chance to win even with one loss.

It produces a Graphviz dot file that will produce an image like below. The black arrows show winners, the red arrows show losers. The black circles are the normal bracket and the red ones are the loser's bracket.

You can also have an arbitrary number of loser's brackets. Here's three, with yellow showing the twice-loser's bracket.

It is also possible to group brackets together visually with group_brackets.