Consider the following code:
$Assumptions =
Element[f, Reals] && Element[\[Beta], Reals] &&
Element[\[Alpha], Reals] && Element[n, Reals] &&
Element[\[Epsilon], Reals] &&
\[Alpha] > 0 && \[Beta] > 0 && \[Mu] > 0 && \[Epsilon] > 0 &&
f > 0 && n > 0
f := 1 - Exp[-\[Beta] (1 - Exp[-\[Alpha]\[Epsilon]])^n]
DSolve[f''[\[Epsilon]] == 0, f[\[Epsilon]], \[Epsilon]]
I get the following error message :
DSolve::ivar: 1-E^(-(1-Power[<<2>>])^n \[Beta]) is not a valid variable.
What is my mistake? What is the correct method?
