The open circles in the decision tree represent points where different random events can happen. We'll call these random nodes. In the AKQ game, the random nodes represent John and Tom's cards: the first random node at the top represents John receiving one of the three cards and the second row of random nodes represents Tom receiving one of the remaining two cards. The probability of each card being dealt is given along the arrows. The solid nodes are decision nodes, where one of the players must choose an action. The only decisions are whether Tom bluffs with Q♠ (at frequency b) and whether John bluffcatches (calls) with K♠ (at frequency c).