I'm a newbie in signal processing. I understand that the discrete convolution operation is used for FIR filters: in the convolution formula `y[n] = x[n] * h[n] = sum(x[k] x h[n-k])`, the right-hand-side obviously does not have `y[n]`. By the definition of this convolution operation, am I correct in assuming that it is **not** used for IIR filters in general, since IIR filters can reference `y[]` on the right-hand-side?