I'm trying to simplify this. I have two functions, f0(z), and f'(t, x, y, z). One is the 'base' value that varies only with height, the other is the small 'perturbation' value that varies with all four variables. I am substituting these into an equation that calls for ∂(f)/∂(x) Do I write this as ∂ (f0 + f' ) / ∂(x) ? And if so, how can I simplify it? Since f0 is not a function of x, can I just cross it out completely? Is it equal to ∂(f0) / ∂(x) + ∂(f') / ∂(x) ?