a. Robbery defined. A person is guilty of robbery if, in the course of committing a theft, he:
(1) Inflicts bodily injury or uses force upon another; or
(2) Threatens another with or purposely puts him in fear of immediate bodily injury; or
(3) Commits or threatens immediately to commit any crime of the first or second degree.
An act shall be deemed to be included in the phrase "in the course of committing a theft" if it occurs in an attempt to commit theft or in immediate flight after the attempt or commission.
b. Grading. Robbery is a crime of the second degree, except that it is a crime of the first degree if in the course of committing the theft the actor attempts to kill anyone, or purposely inflicts or attempts to inflict serious bodily injury, or is armed with, or uses or threatens the immediate use of a deadly weapon.