Functions that are their own inverse.
32575
What's the name for the property of a function $f$ that means $f(f(x))=x$?
78698
Prove if $f$ has a right inverse function: $f\circ g=id_x$ $\iff$ $f$ is onto $Y$
54685
Defining metrics as a function to something other than the reals.
151947
Finding a pair of functions with properties
37122
Modifying some features on the graphs of a function and its inverse
145785
Sets of functions closed within composition.
144557
Linearly independent functionals
1671
Convolution of a function with itself
24126
When functions commute under composition
78844
Inverting a function in a certain region
98559
subtlety of self-defined function and its evaluation
14830
A transformation of F[x]
46698
Showing a set is closed under inverses
125811
Recognizing special cases of a defined function for permuted arguments
44293
Functions satisfying $f\left( f(x)^2+f(y) \right)=xf(x)+y$
29647
Do there exist functions satisfying $f(x+y)=f(x)+f(y)$ that aren't linear?
60306
Natural class of functions whose $\mathcal O$-sets are linearly ordered