Abstract
For any map $f$ from $\mathbb{R}$ to $\mathbb{R}$, if an interval $J$ contains all periodic points of period 1 and 2, then $f(f(J))$ contains all periodic points (and therefore contains the centre of $f$).
Citation
M. Archana. V. Kannan. "Intervals Containing All the Periodic Points." Real Anal. Exchange 41 (2) 263 - 270, 2016.