This Topic continues discussing important signals that are needed to complete the mathematical framework of Fourier analysis and sampling theory. After revising the limiting operation to obtain an impulse, this Topic considers the result of multiplying a signal by an impulse. This product produces another impulse, but where the weight is the signal value. The Topic the  discusses the concept of a signal sampler in terms of multiplying by an impulse and integrating, and then extends the result by introducing the infamous sifting theorem. These important concepts are the basis of Nyquist sampling theory.