In my case that doesnt work as I wanted to perform a Taylor expansion on q depending on f. 

Or is there a neater way to do this?

> restart;
> q := cos(f(x)^2);
                              /    2\
                           cos\f(x) /
> p := subs(f(x) = f, q);
                               / 2\
                            cos\f /
> t := taylor(%, f = 0, 5);
                            1  4    / 8\
                        1 - - f  + O\f /
                            2           
> restart;

> q := cos(f(x)^2);
                              /    2\
                           cos\f(x) /
> alias(f = f(x));
                               f
> taylor(q, f = 0, 5);
%;
Error, invalid input: taylor received f(x) = 0, which is not valid for its 2nd argument, eqn

In my case that doesnt work as I wanted to perform a Taylor expansion on q depending on f. 

Or is there a neater way to do this?

> restart;
> q := cos(f(x)^2);
                              /    2\
                           cos\f(x) /
> p := subs(f(x) = f, q);
                               / 2\
                            cos\f /
> t := taylor(%, f = 0, 5);
                            1  4    / 8\
                        1 - - f  + O\f /
                            2           
> restart;

> q := cos(f(x)^2);
                              /    2\
                           cos\f(x) /
> alias(f = f(x));
                               f
> taylor(q, f = 0, 5);
%;
Error, invalid input: taylor received f(x) = 0, which is not valid for its 2nd argument, eqn

Thanks for your answer

Thanks for your answer

Oh turns out subs can help me out as follows

> p := f(x)^2+g(x)^3;
> q := subs(f(x) = f, g(x) = g, p);