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 __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)
