A witness is a third party who is ordered by the court to state what he has seen or heard in relation to an action, and whatever he has seen or heard may serve as an important basis for discovery of the truth and is non-substitutable. Unless otherwise prescribed by law, every person has the duty to testify before a court. Thus, the Code of Criminal Procedure provides in Article 178, Paragraph 1, that "a lawfully summoned witness who fails to appear without proper reason may be fined a sum of not more than fifty yuan, and in addition thereto may be arrested with a warrant. If he fails to appear when summoned again, the same punishment may be imposed." Discovery of the truth of a case may be achieved through examination of the witness, and is essential to maintaining the social order and increasing the public interest. Like a witness, an informer is a third party other than a "party" in a criminal case. If the court deems it necessary to call an informer to state during the proceeding what he has seen or heard, he may of course be taken as a witness and treated in pursuance of the provision quoted above. Accordingly, our Interpretation No. Yuan-tze 47 holding that Article 95 of the Code of Criminal Procedure then prevailing, i.e., Article 178 of the present Act as amended, may be made applicable to informers is not in conflict with the Constitution.