Is there a known set of closed form solutions to the functional equation f(f(z)) = sin z?
133333
Find $f(x)$ for $f(f(x))=\sin x$
149328
A function such that $f:\mathbb C \to \mathbb C$ such that $f(z)f(iz)=z^2$ satisfies $f(z)+f(-z)=0$.(MADHAVA-2020)
32856
Functional equations $f(x+y)= f(x) + f(y)$ and $f(xy)= f(x)f(y)$
34060
Laurent Series of $f(z) = \sin {\frac{1}{z}}$ at $z=0$
42713
Solutions to the equation $ze^{a-z}=1$
103251
Solution(s) to $f(x + y) = f(x) + f(y)$ (and miscellaneous questions...)
13086
Overview of basic facts about Cauchy functional equation
6680
Solve for all possible functions f: $|f(x)-f(y)|=2|x-y|$.
4178
Solve $f(x)f(2x^2) = f(2x^3+x)$
156778
Finding functions satisfying $f(f(x))+f(x)+x=0$
19474
Find all solutions to the functional equation $f(x) +f(x+y)=y+2 $
62111
Functional Equation $f(mn)=f(m)f(n)$.
34074
Nonlinear Functional Equation $f(x)^{2}=f\left(\frac x a\right)$
67594
Books on functional equations
24810
Functions satisfying $(b-a)f'(\tfrac{a+b}{2}) = f(b)- f(a)$
25953
Solving a functional relation $f\left( x \cdot f(y)\right)=x^2 \cdot y^a$
28148
Are there any simple ways to see that $e^z-z=0$ has infinitely many solutions?