Question: A computer has three registers, A, B and R. It has only three instructions:

A->R : Load R with A

B->R : Load R with B

A-R->A : Subtract R from A and store the result in A

Using these instructions how can you do the follwoing?

B->A : Load A with B

Solution:
A->R
A-R->A // at this point A is zeroed out
B->R
A-R->A // A == -B
A->R // R == -B
A-R->A // A == 0
A-R->A // A == B