Your are right: my question war vague. I did not know what can maple do. Question should be so: I have a composite function f(x(t))=0. First I want the first oder condition with respect to x(t), diff(f(x(t)), x(t)), then diff the result with respect to t. In the first step t is only a parameter, the second step I want to see the effect of t on x when t changes. By replaying your example I find man can direct diff (D(f(x))(x(t)). So I have reached my aims: first define a function f(x), and diff it. (man can not direct compute diff(f(x(t)), x(t)) with maple.) Second rewrite the results df(x)/dx to (D(f(x))(x(t)) und x to x(t), then diff it!! Thanks again to schivnorr, Axel Vogt and dharr.

Hallo Schivnorr, Thanks for your help. You are right for a concret function. In my work I need it in a general form. For example, d(f(x(t))/dt= df/dx*dx/dt. Then I can operate them as a variable with "+" und "*". Can man so do it or not? Thank you. Jahn