# Definition of exact form

That's the definition of exact form in $E$. But if we look at the definition 10.18 we see that $\lambda \in C'$ but Rudin skip this condition.

Can anyone please explain this moment

• It would have been better to be explicit about the differentiability assumptions, I think, but Rudin left them implicit here. He's talking about $d\lambda$, so $\lambda$ has to be a form for which $d\lambda$ makes sense. I don't think Rudin has extended the notion to more general forms in the book, so $\lambda$ would need to be continuously differentiable. – Daniel Fischer May 9 '16 at 18:13
• @DanielFischer, Hello! Can you help please with this? I am dealing with this couple days and no ideas. math.stackexchange.com/questions/1779261/… – ZFR May 10 '16 at 9:20
• @DanielFischer, I would so grateful for your help, Daniel! – ZFR May 10 '16 at 9:28