import string


class SentenceVariable(object):
    symbols = string.ascii_lowercase


class SupportSign(object):
    symbols_open = ['[', '{', '(']
    symbols_close = [']', '}', ')']
    symbols = symbols_open + symbols_close

    @classmethod
    def get_closed_symbol(cls, open_symbol):
        return cls.symbols_close[cls.symbols_open.index(open_symbol)]


class SentenceConjunction(object):
    symbols_conjunction = ['.', '*', '&', '∧', 'AND']
    symbols_alternative = ['+', '∧', 'A', 'OR']
    symbols_implication = ['⇒', '→', '⊃']
    symbols_equivalence = ['⇔', '≡', '↔']
    symbols = symbols_conjunction + symbols_alternative + symbols_implication + symbols_implication


class Negation(object):
    symbols = ['!', '¬', '˜']