def _validate_duplication(self, subj_and_pred, cl):
subj, pred = subj_and_pred<EOL>log.info("<STR_LIT>" % pred)<EOL>if (subj, pred) in self.checked_attributes:<EOL><INDENT>err = self.err("<STR_LIT>",<EOL>self._field_name_from_uri(pred),<EOL>self._field_name_from_uri(cl))<EOL>return ValidationWarning(ValidationResult.WARNING, err['<STR_LIT>'],<EOL>err['<STR_LIT>'], err['<STR_LIT>'])<EOL><DEDENT>
returns error if we've already seen the member `pred` on `subj`