(1) Robbery Defined.  A person is guilty of robbery if, in the course of committing a theft, he:

  (a) inflicts serious bodily injury upon another;  or

  (b) threatens another with or purposely puts him in fear of immediate serious bodily injury;  or

  (c) commits or threatens immediately to commit any felony of the first or second degree.

 An act shall be deemed "in the course of committing a theft" if it occurs in an attempt to commit theft or in flight after the attempt or commission.

 (2) Grading.  Robbery is a felony of the second degree, except that it is a felony 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.