Author/Authors :
- - نويسنده Department of Mathematics, Faculty of Basic Science, Shahed University, Tehran, Iran. Bayatmanesh Elham , - - نويسنده Department of Mathematics, Faculty of Basic Science, Shahed University, Tehran, Iran. Akbari Tootkaboni Mohammad
Abstract :
Let $S$ be a dense subsemigroup of $(0,+infty)$. In this paper, we state definition of thick near zero, and also we will introduce a definition that is equivalent to the definition of piecewise syndetic near zero which presented by Hindman and Leader in cite{Hin-Lead}. We define density near zero for subsets of $S$ by a collection of nonempty finite subsets of $S$ and we investigate the conditions under these concepts.