def __breakdown_sentence(sentence):
sentence = Braces.remove_surrounding(sentence.strip())
replaced = Braces.replace(sentence)
operator = __get_operator(replaced[0])
operands = __get_operands(replaced, operator)
if not operands:
msg = "Could not parse sentence '{0}'".format(sentence)
raise utils.ParsingError(msg)
return (operator, ) + operands
def __breakdown_sentence(sentence):
sentence = Braces.remove_surrounding(sentence.strip())
replaced = Braces.replace(sentence)
operator = __get_operator(replaced[0])
operands = __get_operands(replaced, operator)
if not operands:
msg = "Could not parse sentence '{0}'".format(sentence)
raise utils.ParsingError(msg)
return (operator, ) + operands
def __negation_cnf(operands):
tail = Braces.remove_surrounding(operands[0])
if __is_symbol(tail):
return LogicOperator.Negation + tail
tail_operation = __breakdown_sentence(tail)
operator = tail_operation[0]
tail_operands = tail_operation[1:]
rewritten_formula = ""
if operator == LogicOperator.Negation:
rewritten_formula = tail_operands[0]
elif operator == LogicOperator.Conjuction:
lhs, rhs = tail_operands
pattern = "{2}{0} {3} {2}({1})"
rewritten_formula = pattern.format(lhs, rhs, LogicOperator.Negation,
LogicOperator.Disjunction)
elif operator == LogicOperator.Disjunction:
lhs, rhs = tail_operands
pattern = "{2}({0}) {3} {2}({1})"
rewritten_formula = pattern.format(lhs, rhs, LogicOperator.Negation,
LogicOperator.Conjuction)
elif operator == LogicOperator.Every or operator == LogicOperator.Exists:
negated_operator = LogicOperator.Exists if operator == LogicOperator.Every \
else LogicOperator.Every
variables, expression = tail_operands
pattern = "{0} {1}({2}({3}))"
rewritten_formula = pattern.format(negated_operator, variables,
LogicOperator.Negation, expression)
else:
rewritten_formula = "{0}({1})".format(LogicOperator.Negation,
__compute_cnf(tail))
return __compute_cnf(rewritten_formula)
def __get_operands(replaced_sentence, operator):
text, replacements = replaced_sentence
if operator is None:
return False
if operator == LogicOperator.Negation:
sentence = Braces.restore(text, replacements)
if sentence[0] == operator:
return (sentence[1:], )
return False
if operator == LogicOperator.Every or operator == LogicOperator.Exists:
op_index = text.index(operator)
left_brace = text[op_index:].index(Braces.Left)
variables = text[op_index + 1:left_brace].strip()
expression = replacements[0][1:-1]
return (variables, expression)
lhs, rhs = text.split(" {0} ".format(operator), maxsplit=1)
separator = "!SEPARATOR!"
separated = "{0} {1} {2}".format(lhs, separator, rhs)
lhs, rhs = Braces.restore(separated, replacements).split(separator)
return (lhs.strip(), rhs.strip())
def __get_operands(replaced_sentence, operator):
text, replacements = replaced_sentence
if operator is None:
return False
if operator == LogicOperator.Negation:
sentence = Braces.restore(text, replacements)
if sentence[0] == operator:
return (sentence[1:], )
return False
if operator == LogicOperator.Every or operator == LogicOperator.Exists:
op_index = text.index(operator)
left_brace = text[op_index:].index(Braces.Left)
variables = text[op_index + 1:left_brace].strip()
expression = replacements[0][1:-1]
return (variables, expression)
lhs, rhs = text.split(" {0} ".format(operator), maxsplit=1)
separator = "!SEPARATOR!"
separated = "{0} {1} {2}".format(lhs, separator, rhs)
lhs, rhs = Braces.restore(separated, replacements).split(separator)
return (lhs.strip(), rhs.strip())
def __clean_cnf(cnf, is_first_order):
cnf = Braces.flatten(cnf, is_first_order)
clauses = set()
for disjunct_text in cnf.split(LogicOperator.Conjuction):
disjunct_text = disjunct_text.replace(Braces.Left, "")\
.replace(Braces.Right, "")
if len(disjunct_text) == 0:
continue
disjunct_text = disjunct_text.replace(Braces.FO_Left, Braces.Left)\
.replace(Braces.FO_Right, Braces.Right)
disjunct = frozenset(symbol.strip() for symbol in
disjunct_text.split(LogicOperator.Disjunction))
if not is_disjunction_tautology(disjunct):
clauses.add(disjunct)
return __clean_clauses(clauses)
def __clean_cnf(cnf, is_first_order):
cnf = Braces.flatten(cnf, is_first_order)
clauses = set()
for disjunct_text in cnf.split(LogicOperator.Conjuction):
disjunct_text = disjunct_text.replace(Braces.Left, "")\
.replace(Braces.Right, "")
if len(disjunct_text) == 0:
continue
disjunct_text = disjunct_text.replace(Braces.FO_Left, Braces.Left)\
.replace(Braces.FO_Right, Braces.Right)
disjunct = frozenset(
symbol.strip()
for symbol in disjunct_text.split(LogicOperator.Disjunction))
if not is_disjunction_tautology(disjunct):
clauses.add(disjunct)
return __clean_clauses(clauses)
def __negation_cnf(operands):
tail = Braces.remove_surrounding(operands[0])
if __is_symbol(tail):
return LogicOperator.Negation + tail
tail_operation = __breakdown_sentence(tail)
operator = tail_operation[0]
tail_operands = tail_operation[1:]
rewritten_formula = ""
if operator == LogicOperator.Negation:
rewritten_formula = tail_operands[0]
elif operator == LogicOperator.Conjuction:
lhs, rhs = tail_operands
pattern = "{2}{0} {3} {2}({1})"
rewritten_formula = pattern.format(lhs, rhs,
LogicOperator.Negation,
LogicOperator.Disjunction)
elif operator == LogicOperator.Disjunction:
lhs, rhs = tail_operands
pattern = "{2}({0}) {3} {2}({1})"
rewritten_formula = pattern.format(lhs, rhs,
LogicOperator.Negation,
LogicOperator.Conjuction)
elif operator == LogicOperator.Every or operator == LogicOperator.Exists:
negated_operator = LogicOperator.Exists if operator == LogicOperator.Every \
else LogicOperator.Every
variables, expression = tail_operands
pattern = "{0} {1}({2}({3}))"
rewritten_formula = pattern.format(negated_operator,
variables,
LogicOperator.Negation,
expression)
else:
rewritten_formula = "{0}({1})".format(LogicOperator.Negation,
__compute_cnf(tail))
return __compute_cnf(rewritten_formula)
