Two players, A and B.
The strategy space for A is { a1, a2};
The strategy space for B is {b1, b2, b3, b4}.
The expected payoff  for A to employ strategy a1 is
Ea[a1] = P1*U(a1,b1)+P2*U(a1,b2)+P3*U(a1,b3)+P4*U(a1,b4)
Ea[a2] = P1*U(a2,b1)+P2*U(a2,b2)+P3*U(a2,b3)+P4*U(a2,b4)
The ensure A is indifferent  to a1 and a2, we have
Ea[a1] = Ea[a2]
Another trivial equation is p1+p2+p3+p4 = 1.
我的问题是我们有四个变量: p1, p2, p3 and p4, 但只有两个方程。 在这样的情况下
，如何求mixed strategy呢？