Function such that $f(f(f(x))) = f(f(x)) \neq f(x)$
91211
Calculus function create
29647
Do there exist functions satisfying $f(x+y)=f(x)+f(y)$ that aren't linear?
20199
Find a surjective function $f:\mathbb{N}\to \mathbb{Q}$
50111
non-continuous function satisfies $f(x+y)=f(x)+f(y)$
57938
When do two functions become equal?
106748
Number of functions $f : A \to A$ such that $f(f(x))=f(x)$
110704
Find all functions $f$ such that $f(x)+f(\frac{1}{1-x})=x$
50552
find functions that $f(m+k)=f(mk-n)$
127887
Existence of a meromorphic functions $f(z)$ such that $|f(z)|\geq |z|$.
113740
Find a uniformly continuous function such that $a_{n+1}=f(a_n)$
28011
Does there exists an entire function such that for each $|z|>C$ for some constant $C$, $|f(z)|=|z|+1$?
12556
A non-trivial, non-negative, function bounded below by its derivative with $f(0)=0$?
117716
Condition on function $f:\mathbb{R}\rightarrow \mathbb{R}$ so that $(a,b)\mapsto | f(a) - f(b)|$ generates a metric on $\mathbb{R}$
142682
Find $f(x)$ where $ f(x)+f\left(\frac{1-x}x\right)=x$
139019
Polynomial satisfying $f(x) = f'(x) \cdot f''(x)$
17154
Does a non-trivial solution exist for $f'(x)=f(f(x))$?
81720
$f(x) + f(x+f(y)) = y + f(f(x) + f(f(y)))$