Heuristic 4

The main objective is to find chi in the equation, `chi.diff(x)  + h*chi.diff(y) - h.diff(y)*chi = 0` , and find the infintesimals by setting one of xi and eta in the equation, `eta = xi*h + chi` depending upon the simplicity. The first part has been done, I am working on the second part. @flacjacket