Sharkovskii's theorem

== English == === Alternative forms === Sharkovsky's theorem, Sharkovskiy's theorem, Sarkovskii's theorem === Etymology === Named after Oleksandr Mikolaiovich Sharkovsky. === Proper noun === Sharkovskii's theorem (mathematics) A theorem about discrete dynamical systems. One of its implications is that if a discrete dynamical system on the real line has a periodic point of period 3, then it must have periodic points of every other period.