The decision nodes for \(A\) and \(B\) respectively are \(V_A=\{v_1, v_3\}\) and \(V_B=\{v_2\}\); and the outcome nodes are \(O=\{o_1, o_2, o_3, o_4\}\). The labels of the edges in the above tree are the actions available to each player. For instance, \(Act(v_1)=\{O_1, I_1\}\). There are four strategies for \(A\) and two strategies for \(B\). To simplify notation, we denote the players’ strategies by the sequence of choices at each of their decision nodes. For example, \(A\)’s strategy \(s_A^1\) defined as \(s_A^1(v_1)=O_1\) and \(s_A^1(v_3)=O_3\) is denoted by the sequence \(O_1O_3\). Thus, \(A\)’s strategies are: \(s_A^1=O_1O_3\), \(s_A^2=O_1I_3\), \(s_A^3=I_1O_3\) and \(s_A^4=I_1I_3\). Note that \(A\)’s strategy \(s_A^2\) specifies a move at \(v_3\), even though the earlier move at \(v_1\), \(O_1\), means that \(A\) will not be given a chance to move at \(v_3\). Similarly, Bob’s strategies will be denoted by \(s_B^1=O_2\) and \(s_B^2=I_2\), giving the actions chosen by \(B\) at his decision node. Then, for example, \(out(v_2,(s_A^2, s_B^2))=o_4\). Finally, if \(X=\{s_A^1, s_A^4\}\), then \(Out_B(v_2,s_B^2, X)=\{o_3, o_4\}\).