Obtain the impulse responses of the following systems
(a) The ideal delay system. y[n] = x[n-nd]
(b) The accumulator system. y[n] = sum (xk) , k from -inf to n
(c) Forward difference system. y[n] = x[n + 1]- x[n] (d) Backward difference system. y[n] = x[n]- x[n - 1]