Post's inversion theorem 
Post's inversion theorem is a difficult method of inverting this operation. Performing this operation on the probability density function of a distribution is an easy way of deriving the distribution's moment-generating function. This function takes a differential equation with constant coefficients to a polynomial, and in circuit theory it's useful to (*) take circuit elements to impedances in the s-domain. This linear function is defined as the integral from zero to infinity of the product of e to the negative s times t times the input function, dt. For 10 points, name this operation named for a Frenchman, a useful transform.
Post's inversion theorem is a difficult method of inverting this operation.
Laplace transform