 Core interval of an expanding tent map

For $T_s(x)=1-s|x|$ with $1<s\le 2$, the largest closed interval mapped onto itself is $A=[1-s,1]=[T_s^2(0),T_s(0)]$. It equals the image of $[-1,1]$. Every point outside $A$ enters $A$ after one iterate, because $T_s([-1,1])=A$. It subsequently remains in $A$.

// Target: dynamical-systems.bigb