docs: def from_str(cls, string):
          """
          Creates a literal from a string
  
          Parameters
          ----------
          string : str
              If the string starts with '!', it's interpreted as a negated variable
  
          Returns
          -------
          caspo.core.literal.Literal
              Created object instance
          """
          if string[0] == '!':
              signature = -1
              variable = string[1:]
          else:
              signature = 1
              variable = string
  
          return cls(variable, signature)