Distinguish between the following: A 'writ of mandamus' and a 'writ of certiorari'.

The writ of mandamus is a command issued to direct any person, corporation, inferior Court or Government authority requiring him to do a particular thing therein specified which pertains to his or their office and is further in the nature of a public duty. This writ is used when the inferior tribunal has declined to exercise jurisdiction. Mandamus can be issued against any public authority. The applicant must have a legal right to the performance of a legal duty by the person against whom the writ is prayed. Mandamus is not issued if the public authority has discretion. Mandamus can be issued by the Supreme Court and all the High Courts to all authorities. It is a discretionary remedy and the Court may refuse if alternative remedy exists except in case of infringement of Fundamental Rights. The writ of certiorari is available to any person whenever any body of persons having legal authority to determine questions affecting the rights of subjects and having the duty to act judicially, acts in excess of its legal authority. The writ removes the proceedings from such body to the High Court in order to quash a decision that goes beyond the jurisdiction of the deciding authority.