Separator functions for homomorphic filtering

A procedure is presented to test an arbitrary function of two variables N(x, y) to see if a separator function exists such that S[N(x, y)] = A (x) + B(y). If so, the procedure evaluates S[.],A,B. Necessary conditions for the existence of S[.] are established and some limitations are given in a theorem on sufficient conditions. Examples and a canonic representation of the test and procedure are also presented.