def _add_to_reading_list(self, glueformula, reading_list):
        add_reading = True
        if self.remove_duplicates:
            for reading in reading_list:
                try:
                    if reading.equiv(glueformula.meaning, self.prover):
                        add_reading = False
                        break;
                except Exception, e:
                    #if there is an exception, the syntax of the formula  
                    #may not be understandable by the prover, so don't
                    #throw out the reading.
                    print 'Error when checking logical equality of statements', e
                    pass
        if add_reading:
            reading_list.append(glueformula.meaning)