A student writes:

        Dr. Patt,

        For the shift operations, can the amount to be shifted 
	be a negative number?
	
	<<name withheld to protect one who wants us to be precise>>

Thank you for the question.  Just when I think everything is clear, you point 
out an ambiguity.  Given the essence of the instruction, we need to be able to 
shift right or left 15 positions, and so with four bits it better be the case 
that we are using a non-negative integer code.  But you are just starting your 
education in computer architecture, and so we should have made it explicit.

Yale Patt