Neighbourhoods, Classes and Near Sets

Sufficiently Near Sets of Neighbourhoods

The focus of this paper is on sets of neighbourhoods that are sufficiently near each other as yet another way to consider near sets. This study has important implications in M. Katětov’s approach to topologising a set. A pair of neighbourhoods of points are sufficiently near, provided that the C̆ech distance between the neighbourhoods is less than some number ε. Sets of neighbourhoods are suffic...

Some Results on Topological Neighbourhoods

Full proofs of results announced here are to be found in [lO]. We consider the problem of classifying germs of neighbourhoods of locally flat topological submanifolds. Let M be a fixed topological manifold. An r-neighbourhood of M is a pair (i, N) where N is a topological manifold of dimension n+r and i:M—*N a locally flat embedding satisfying i^ÇdN) —dM. Denote the set of germs of r-neighbourh...

On Hereditary Helly Classes of Graphs

In graph theory, the Helly property has been applied to families of sets, such as cliques, disks, bicliques, and neighbourhoods, leading to the classes of clique-Helly, disk-Helly, biclique-Helly, neighbourhood-Helly graphs, respectively. A natural question is to determine for which graphs the corresponding Helly property holds, for every induced subgraph. This leads to the corresponding classe...

Semi-θ-Open Sets and New Classes of Maps

On Pre-θ-Open Sets and Two Classes of Functions