How can I make the LAST_NAME and FIRST_NAME fields unique? So there can’t be two people with the same first and last names.

Code:
CREATE TABLE ROT_MachineUsers 
   (MU_ID Int PRIMARY KEY,
   COMP_ID Varchar(10) UNIQUE NOT NULL,
   LAST_NAME Varchar(40) NOT NULL,
   FIRST_NAME Varchar(40) NOT NULL);