Is there a function $f(x)$ such that $f(f(x))=e^x$?
26677
thoughts about $f(f(x))=e^x$
44293
Functions satisfying $f\left( f(x)^2+f(y) \right)=xf(x)+y$
10068
$f(x,y)= e^{-\frac{1}{x^2+y^2}}$ when $(x,y)\neq (0,0)$ and $f(0,0)=0$.
17154
Does a non-trivial solution exist for $f'(x)=f(f(x))$?
24810
Functions satisfying $(b-a)f'(\tfrac{a+b}{2}) = f(b)- f(a)$
55492
Existence of $f'\in F$ such that $f^{[G:F]}=(f')^n$ for finite extension $F\subset G$
40047
Is $\int_a^b f(x) dx = \int_{f(a)}^{f(b)} f^{-1}(x) dx$?
114307
Are Exponential and Trigonometric Functions the Only Non-Trivial Solutions to $F'(x)=F(x+a)$?
132113
Does $f(x) = f(2x)$ for all real $x$, imply that $f(x)$ is a constant function?
89257
Give an example of a function $f:\mathbb{R}^2 \mapsto \mathbb{R}^2$ such that
39090
Finding functions such that $f(g(x)) = f(x)g(x)$
156778
Finding functions satisfying $f(f(x))+f(x)+x=0$
99894
Does there exists an entire function $f$ such that $f(0)=1$ and $|f(z)|\leq \frac{1}{|z|} $ for all $|z|\geq 5$?
60348
How do I prove $F(a)=F(a^2)?$
23186
$f: \mathbb{R^2} \to \mathbb{R}$ a $C^\infty$ function such that $f(x,0)=f(0,y)=0$ then exists $g$ such that $f(x,y)=xy\, g(x,y)$
72769
How find this function $xf(x^2)=f(x),x>0$
80199
Do we have always $f(A \cap B) = f(A) \cap f(B)$?