Unexpectedly 'Derivative' function in CAS got the wrong answer!
When I plugin f(sec(x)) inside the Derivative function where f is an arbitrary function, sec is reciprocal of the cosine function.
Derivative(f(sec(x)),x) returns (sin(x) * f'(1 / cos(x) / (cos(x))^(2))) instead of (sin(x) / (cos(x))^(2) * f'(1 / cos(x)))
By applying the chain rule /cos(x)^2 should be outside the f' function not inside as CAS return.
You can check wolfram alpha if this isn't clear.
I hope you get the idea.