X1   X2.O      X2.Y     out
-------------------------------------
        0      1        0      0
        0      0        1      0
        1      1        0      0
        1      0        0      0
        1      1        0      0
-------------------------------------
        0      1        0      1
        1      0        0      1
        0      1        0      1
        1      0        0      1
        1      0        1      1
=====================================
Prob   0.6    0.5      0.2    0.5
P(S)   0.6    0.4      0.2
P(-S)  0.6    0.6      0.2
=====================================