Let $f$ be a continuous function on $\Bbb R$ satisfying $f(f(f(x)))=x ;\ \forall x \in \Bbb R$. Then is $f$ the identity function?
$f:\mathbb R \to \mathbb R$ be a continuous such that $f(f(f(x)))=x,\forall x \in \mathbb R$ , is $f(x)=x , \forall x \in \mathbb R$?