I am using Maple to generate PDEs. I have expressions of the form p(dx,dy,dz, etc.) where p is a nonlinear polynomial. I would like to substitute d/dx for dx etc and then later apply the resulting differential equation to a function. I am having multiple problems with this.

1. Maple seems to be unable to handle a derivative unless there is a function for the derivative to act on. (This is not a huge issue, but it would be helpful.)

2. Even if I do specify a function Maple maps dx^3 to diff(f,x...