Which writ commands a public authority to perform a duty it has failed to perform?

Explanation

1. 01

   Mandamus means 'we command', and it orders a public authority to do the duty the law places on it.

2. 02

   It cannot be issued to compel a discretionary act, only a duty.

3. 03

   Certiorari quashes an order already made by a lower court, while prohibition stops one before it is made.