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Dynamical systems arising by iterated functions on arbitrary semigroups

  • M. Akbari Tootkaboni,
  • A. R. Bagheri Salec,
  • S. Abbas

摘要

Let S be a discrete semigroup and let \(^SS\) S S denote the collection of all functions \(f:S\rightarrow S\) f : S S . If \((P,\circ )\) ( P , ) is a subsemigroup of \(^SS\) S S by composition operation, then P induces a natural topological dynamical system. In fact, \((\beta S,\{T_f\}_{f\in P})\) ( β S , { T f } f P ) is a topological dynamical system, where \(\beta S\) β S is the Stone–Čech compactification of S, \(x\mapsto T_f(x)=f^\beta (x):\beta S\rightarrow \beta S\) x T f ( x ) = f β ( x ) : β S β S and \(f^\beta \) f β is a unique continuous22 extension of f. In this paper, we concentrate on the dynamical system \((\beta S,\{T_f\}_{f\in P})\) ( β S , { T f } f P ) , when S is an arbitrary discrete semigroup and P is a subsemigroup of \(^SS\) S S and obtain some relations between subsets of S and subsystems of \(\beta S\) β S with respect to P. As a consequence, we prove that if \((S,+)\) ( S , + ) is an infinite commutative discrete semigroup and \(\mathcal {C}\) C is a finite partition of S, then for every finite number of arbitrary homomorphisms \(g_1,\dots ,g_l:\mathbb {N}\rightarrow S\) g 1 , , g l : N S , there exist an infinite subset B of the natural numbers and \(C\in \mathcal {C}\) C C such that for every finite summations \(n_1,\dots , n_k\) n 1 , , n k of B there exists \(s\in S\) s S such that \(\begin{aligned} \{s+g_i(n_1),s+g_i(n_2),\dots , s+g_i(n_k)\}\subseteq C,\,\,\,\,\,\,\forall i\in \{1,\dots ,l\}. \end{aligned}\) { s + g i ( n 1 ) , s + g i ( n 2 ) , , s + g i ( n k ) } C , i { 1 , , l } .