def x_and_not_y():
# remember:
# 2 = !(x & !y)
# -2 = x & !y
ordering = {'x': 0, 'y': 1}
g = BDD(ordering)
u = 3
v = -1
w = 1
t = (1, v, w)
g._succ[u] = t
g._pred[t] = u
g._ref[abs(v)] += 1
g._ref[abs(w)] += 1
g._ref[abs(u)] = 0
u = 2
v = 1
w = 3
t = (0, v, w)
g._succ[u] = t
g._pred[t] = u
g._ref[abs(v)] += 1
g._ref[abs(w)] += 1
g._ref[abs(u)] = 0
g._min_free = 4
return g
def x_and_not_y():
# remember:
# 2 = !(x & !y)
# -2 = x & !y
ordering = {'x': 0, 'y': 1}
g = BDD(ordering)
u = 3
v = -1
w = 1
t = (1, v, w)
g._succ[u] = t
g._pred[t] = u
g._ref[abs(v)] += 1
g._ref[abs(w)] += 1
g._ref[abs(u)] = 0
u = 2
v = 1
w = 3
t = (0, v, w)
g._succ[u] = t
g._pred[t] = u
g._ref[abs(v)] += 1
g._ref[abs(w)] += 1
g._ref[abs(u)] = 0
g._min_free = 4
return g
def two_vars_xy():
ordering = {'x': 0, 'y': 1}
g = BDD(ordering)
u = 2
t = (0, -1, 1)
g._succ[u] = t
g._pred[t] = u
g._ref[u] = 1
u = 3
t = (1, -1, 1)
g._succ[u] = t
g._pred[t] = u
g._ref[u] = 1
g._min_free = u + 1
return g
def two_vars_xy():
ordering = {'x': 0, 'y': 1}
g = BDD(ordering)
u = 2
t = (0, -1, 1)
g._succ[u] = t
g._pred[t] = u
g._ref[u] = 1
u = 3
t = (1, -1, 1)
g._succ[u] = t
g._pred[t] = u
g._ref[u] = 1
g._min_free = u + 1
return g
