As it is well known every continuous function has the intermediate value property, but even some discontinuous functions like
f(x)={sin(1x)x≠00x=0
are having this property.
In fact we know that a derivative always have this property.
My question is, if for every function f with the intermediate value property exists a function F such that F′=f. And if so, is F unique (up to a constant you may add)?
My attempts till now: (Just skip them if you feel so)
The most natural way of finding those functions would be integrating, so I guess the question can be reduced to, if functions with the intermediate value property can be integrated.
This one depends heavy on how you define when a functions is integrable, we (my analysis class) said that we call a function integrable when it is a regulated function (the limits x→x+0f(x) and x→x−0f(x) exists ) .
As my example above shows, not every function with the intermediate value property is a regulated function. But if we say a function is integrabel when every riemann sum converges the above function is integrable, so it seems like this would be a better definition for my problem.
Edit: As Kevin Carlson points out in a commentar that being a derivative is different from being riemann integrable, he even gave an example for a function which is differentiable but it's derivative is not riemann integrable. So we can't show that those functions are riemann integrable as they are not riemann integrable in general. Now I have no clue how to find an answer.
Answer
If you compose tan−1 with Conway’s Base-13 Function, then you get a bounded real-valued function on the open interval (0,1) that satisfies the Intermediate Value Property but is discontinuous at every point in (0,1). Therefore, by Lebesgue’s theorem on the necessary and sufficient conditions for Riemann-integrability, this function is not Riemann-integrable on any non-degenerate closed sub-interval of (0,1).
Now, it cannot be the derivative of any function either, because by the Baire Category Theorem, if a function defined on an open interval has an antiderivative, then the function must be continuous on a dense set of points. This thread may be of interest to you. :)
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