def distribute_and_over_or(s):
"""Given a sentence s consisting of conjunctions and disjunctions
of literals, return an equivalent sentence in CNF.
>>> distribute_and_over_or((A & B) | C)
((A | C) & (B | C))
"""
s = expr(s)
if s.op == '|':
s = associate('|', s.args)
if s.op != '|':
return distribute_and_over_or(s)
if len(s.args) == 0:
return False
if len(s.args) == 1:
return distribute_and_over_or(s.args[0])
conj = first(arg for arg in s.args if arg.op == '&')
if not conj:
return s
others = [a for a in s.args if a is not conj]
rest = associate('|', others)
return associate('&',
[distribute_and_over_or(c | rest) for c in conj.args])
elif s.op == '&':
return associate('&', list(map(distribute_and_over_or, s.args)))
else:
return s
def actions(self, state):
"""Return a list of applicable actions: nonconflicting
assignments to an unassigned variable."""
if len(state) == len(self.variables):
return []
else:
assignment = dict(state)
var = first([v for v in self.variables if v not in assignment])
return [(var, val) for val in self.domains[var]
if self.nconflicts(var, val, assignment) == 0]
def occur_check(var, x, s):
"""Return true if variable var occurs anywhere in x
(or in subst(s, x), if s has a binding for x)."""
if var == x:
return True
elif is_variable(x) and x in s:
return occur_check(var, s[x], s)
elif isinstance(x, Expr):
return (occur_check(var, x.op, s) or occur_check(var, x.args, s))
elif isinstance(x, (list, tuple)):
return first(e for e in x if occur_check(var, e, s))
else:
return False
def first_unassigned_variable(assignment, csp):
"""The default variable order."""
return first([var for var in csp.variables if var not in assignment])
def ask(self, query):
"""Return a substitution that makes the query true, or, failing that, return False."""
return first(self.ask_generator(query), default=False)