X(t+1) = (A'+B).(A+X)
Y(t+1) = (A+X).(A'+Y)
Z = Y

X   Y   A   B   X   Y   Z
0   0   0   0
0   0   0   1
0   0   1   0
0   0   1   1
0   1   0   0
0   1   0   1
0   1   1   0
0   1   1   1
1   0   0   0
1   0   0   1
1   0   1   0
1   0   1   1
1   1   0   0
1   1   0   1
1   1   1   0
1   1   1   1