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CSC 236               Tutorial Exercises for Week  8              Fall 2007
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Prove that the following algorithm is correct, with respect to the
conditions given.

    Precondition:  x in R, y in N
    Postcondition:  pow(x,y) returns x^y (with convention 0^0 = 1)

    pow(x, y):
        if y == 0:
            return 1
        elif y % 2 == 0:
            t = pow(x, y/2)
            return t * t
        else:
            t = pow(x, (y-1)/2)
            return t * t * x