On topological entropy: when positivity implies +innity Sergiy Kolyada dedicated to my Friend Lluis ALSEDA, based on a joint work with Julia SEMIKINA Max Planck Institute for Mathematics, Bonn and Institute of Mathematics, NASU, Kyiv 4th October 2014 Tossa de Mar, Girona Spain Sergiy Kolyada On topological entropy: when positivity implies +innity Lubo, Lluis, Jaume and S. (Bellaterra, 1993) Sergiy Kolyada On topological entropy: when positivity implies +innity JULIA SEMIKINA Sergiy Kolyada On topological entropy: when positivity implies +innity and possible values of the topological entropy of its elements (continuous maps and homeomorphisms, respectively). 1.Introduction and main results The main topic of our research is to study the relations between the properties of the topological semigroup S(X ) of all continuous maps from X to X (the topological group H(X ) of all homeomorphisms on X ) Sergiy Kolyada On topological entropy: when positivity implies +innity 1.Introduction and main results The main topic of our research is to study the relations between the properties of the topological semigroup S(X ) of all continuous maps from X to X (the topological group H(X ) of all homeomorphisms on X ) and possible values of the topological entropy of its elements (continuous maps and homeomorphisms, respectively). Sergiy Kolyada On topological entropy: when positivity implies +innity when does a compact metric space admit a continuous map (homeomorphism) with positive topological entropy? when does the existence of a positive-entropy continuous map on a compact metric space imply the existence of a +1-entropy continuous map? 1.Introduction and main results More precisely, mostly we will consider the following two questions: Sergiy Kolyada On topological entropy: when positivity implies +innity when does the existence of a positive-entropy continuous map on a compact metric space imply the existence of a +1-entropy continuous map? 1.Introduction and main results More precisely, mostly we will consider the following two questions: when does a compact metric space admit a continuous map (homeomorphism) with positive topological entropy? Sergiy Kolyada On topological entropy: when positivity implies +innity 1.Introduction and main results More precisely, mostly we will consider the following two questions: when does a compact metric space admit a continuous map (homeomorphism) with positive topological entropy? when does the existence of a positive-entropy continuous map on a compact metric space imply the existence of a +1-entropy continuous map? Sergiy Kolyada On topological entropy: when positivity implies +innity Theorem 2 (Semigroups representation) Let S be a monoid (semigroup with identity). Then there exist: 1) a compact Hausdor space X such that the monoid of all nonconstant maps of X into itself is isomorphic to S; 2) a connected metric space X such that S is isomorphic to the semigroup of all quasi-local homeomorphisms of X . 1.Introduction and main results Theorem 1 (Groups representation) Let G be an arbitrary group. Then there exists a connected, locally connected,complete metric space X (or alternatively compact, Hausdor) for which the group of all autohomeomorphisms H(X ) is isomorphic to G. Sergiy Kolyada On topological entropy: when positivity implies +innity 2) a connected metric space X such that S is isomorphic to the semigroup of all quasi-local homeomorphisms of X . 1.Introduction and main results Theorem 1 (Groups representation) Let G be an arbitrary group. Then there exists a connected, locally connected,complete metric space X (or alternatively compact, Hausdor) for which the group of all autohomeomorphisms H(X ) is isomorphic to G. Theorem 2 (Semigroups representation) Let S be a monoid (semigroup with identity). Then there exist: 1) a compact Hausdor space X such that the monoid of all nonconstant maps of X into itself is isomorphic to S; Sergiy Kolyada On topological entropy: when positivity implies +innity 1.Introduction and main results Theorem 1 (Groups representation) Let G be an arbitrary group. Then there exists a connected, locally connected,complete metric space X (or alternatively compact, Hausdor) for which the group of all autohomeomorphisms H(X ) is isomorphic to G. Theorem 2 (Semigroups representation) Let S be a monoid (semigroup with identity). Then there exist: 1) a compact Hausdor space X such that the monoid of all nonconstant maps of X into itself is isomorphic to S; 2) a connected metric space X such that S is isomorphic to the semigroup of all quasi-local homeomorphisms of X . Sergiy Kolyada On topological entropy: when positivity implies +innity Aida B. Paalman-de Miranda, Johannes de Groot, Vera Trnkova 1.Introduction and main results Let X ; Y be topological spaces. A mapping f : X ! Y is called quasi-local homeomorphism if it is continuous and if for each opene set O ⊂ X there exists an open set U ⊂ O such that f jU is a homeomorphism of U onto f (U). Sergiy Kolyada On topological entropy: when positivity implies +innity 1.Introduction and main results Let X ; Y be topological spaces. A mapping f : X ! Y is called quasi-local homeomorphism if it is continuous and if for each opene set O ⊂ X there exists an open set U ⊂ O such that f jU is a homeomorphism of U onto f (U). Aida B. Paalman-de Miranda, Johannes de Groot, Vera Trnkova Sergiy Kolyada On topological entropy: when positivity implies +innity the metric du of uniform convergence (for H(X )): d sup max d −1 x −1 x d x x . u('; ) = x2X f (' ( ); ( )); ('( ); ( ))g The corresponding space will be denoted by Hu(X ). the metric dU of uniform convergence: d sup d x x . The corresponding spaces U ('; ) = x2X ('( ); ( )) will be denoted by HU (X ) and SU (X ). Note that dU ('; ) is well dened for any bounded selfmaps of X (in fact, for any selfmaps of X , since X is bounded). 1.Introduction and main results Given a compact metric space (X ; d), the set (group) H(X ) of all self-homeomorphisms of X , and the set (semigroup) S(X ) of all continuous maps from X to X , we will consider the following metrics on these sets: Sergiy Kolyada On topological entropy: when positivity implies +innity the metric dU of uniform convergence: d sup d x x . The corresponding spaces U ('; ) = x2X ('( ); ( )) will be denoted by HU (X ) and SU (X ). Note that dU ('; ) is well dened for any bounded selfmaps of X (in fact, for any selfmaps of X , since X is bounded). 1.Introduction and main results Given a compact metric space (X ; d), the set (group) H(X ) of all self-homeomorphisms of X , and the set (semigroup) S(X ) of all continuous maps from X to X , we will consider the following metrics on these sets: the metric du of uniform convergence (for H(X )): d sup max d −1 x −1 x d x x . u('; ) = x2X f (' ( ); ( )); ('( ); ( ))g The corresponding space will be denoted by Hu(X ). Sergiy Kolyada On topological entropy: when positivity implies +innity 1.Introduction and main results Given a compact metric space (X ; d), the set (group) H(X ) of all self-homeomorphisms of X , and the set (semigroup) S(X ) of all continuous maps from X to X , we will consider the following metrics on these sets: the metric du of uniform convergence (for H(X )): d sup max d −1 x −1 x d x x . u('; ) = x2X f (' ( ); ( )); ('( ); ( ))g The corresponding space will be denoted by Hu(X ). the metric dU of uniform convergence: d sup d x x . The corresponding spaces U ('; ) = x2X ('( ); ( )) will be denoted by HU (X ) and SU (X ). Note that dU ('; ) is well dened for any bounded selfmaps of X (in fact, for any selfmaps of X , since X is bounded). Sergiy Kolyada On topological entropy: when positivity implies +innity 1.Introduction and main results the Hausdor metric dH (derived from the metric dmax((x1; y1); (x2; y2)) = maxfd(x1; x2); d(y1; y2)g in X × X ) applied to the graphs of maps (we identify a map and its graph, so we will write dH ('; )). The corresponding spaces will be denoted by HH (X ) and SH (X ). Sergiy Kolyada On topological entropy: when positivity implies +innity This is a metric on the family of all bounded, nonempty closed subsets of X . Note that if X is compact we can apply this metric to (the graphs of) continuous maps from X to X . 1.Introduction and main results Recall that the Hausdor distance dH between two sets A1 and A2 in a metric space X is given by dH (A1; A2) = inff" > 0 : B"[A1] ⊇ A2 and B"[A2] ⊇ A1g ; where B"[A] denote the union of all closed balls of radius " > 0 whose centers run over the elements of A. Sergiy Kolyada On topological entropy: when positivity implies +innity 1.Introduction and main results Recall that the Hausdor distance dH between two sets A1 and A2 in a metric space X is given by dH (A1; A2) = inff" > 0 : B"[A1] ⊇ A2 and B"[A2] ⊇ A1g ; where B"[A] denote the union of all closed balls of radius " > 0 whose centers run over the elements of A. This is a metric on the family of all bounded, nonempty closed subsets of X . Note that if X is compact we can apply this metric to (the graphs of) continuous maps from X to X . Sergiy Kolyada On topological entropy: when positivity implies +innity and for any '; 2 S(X ) we have dH ('; ) ≤ dU ('; ). If X is a compact metric space then the topologies given by the uniform metric and Hausdor metric are equivalent in H(X ) and in S(X ). 1.Introduction and main results For any '; 2 H(X ) we have dH ('; ) ≤ dU ('; ) ≤ du('; ) Sergiy Kolyada On topological entropy: when positivity implies +innity If X is a compact metric space then the topologies given by the uniform metric and Hausdor metric are equivalent in H(X ) and in S(X ).