Multiplication in the Fourier domain is convolution in the time domain. Fourier-domain division is time-domain deconvolution. In chapter we encountered the polynomial-division feedback operation X(Z)=Y(Z)/F(Z). This division is challenging when F has observational error. By switching from the Z-domain to the -domain we avoid needing to know if F is minimum phase. The -domain has pitfalls too, however. We may find for some real that vanishes, so we cannot divide by that F. Failure erupts if zero division occurs. More insidious are the poor results we obtain when zero division is avoided by a near miss.