Topology and its Applications, ( ISI ), Volume (158), No (13), Year (2011-6) , Pages (1607-1614)

Title : ( On the homotopy groups of separable metric spaces )

Authors: Fateme Helen Ghane Ostadghassemi , hadi passandideh , Zainab Hamed Labbafian ,

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Abstract

The aim of this paper is to discuss the homotopy properties of locally well-behaved spaces. First, we state a nerve theorem. It gives sufficient conditions under which there is a weak n-equivalence between the nerve of a good cover and its underlying space. Then we conclude that for any (n − 1)-connected, locally (n − 1)-connected compact metric space X which is also n-semilocally simply connected, the nth homotopy group of X, πn(X), is finitely presented. This result allows us to provide a new proof for a generalization of Shelah’s theorem (Shelah, 1988 [18]) to higher homotopy groups (Ghane and Hamed, 2009 [8]). Also, we clarify the relationship between two homotopy properties of a topological space X, the property of being n-homotopically Hausdorff and the property of being n-semilocally simply connected. Further, we give a way to recognize a nullhomotopic 2-loop in 2-dimensional spaces. This result will involve the concept of generalized dendrite which introduce here. Finally, we prove that each 2-loop is homotopic to a reduced 2-loop.

Keywords

, Nerve Homotopy group n, semilocally simply connected space n, connected space Locally n, connected space