New posts in Functional Equations

Given functions $h,k:\Bbb R\to \Bbb R$, is it possible to determine whether $f,g:\Bbb R\to\Bbb R$ exist so that $g\circ f=h$ and $f\circ g=k$?

Given $f(i, j) = f(i − 1, j − 1) + f(i, j − 1)$, find the value of $f(1009, 2019)$

Is my solution correct in terms of proof? I can't prove directly that $f(x)=4$.

Functional equation $f(x+y)=f(x)f(y)-f(xy)+1$

Suppose $f(x)-f(y)=h(g(x)-g(y))$, then $h$ is linear?

Solutions to the functional equation $f(f(x))=f(x+1)$

The Functional Equation $ ( x + y ) \big( f ( x ) - f ( y ) \big) = ( x - y ) f ( x + y ) $, need solution have answer

What is the function $f(x)$ which is differentiable everywhere and $f(x-1)f(x-2)+1=f(x)$?

Dirac delta solutions

Solving the functional equation $f(x)f(y)=c\,f(\sqrt{x^{2}+y^{2}})$