def get_subseq(s, op):
    """Returns the subsequent sequence of applying (op) on the
       sequence 's', in such a way that 'new[i] = old[i+1] (op) old[i]'.
       For example:
        op = lambda a, b: b - a
           → then a difference sequence is returned:
             new[i] = old[i+1] - old[i]
        
        op = lambda a, b: b / a
           → then a division sequence is returned:
             new[i] = old[i+1] / old[i]
        """
    return [op(s[i-1], s[i]) for i in range(1, len(s))]