There are actually more than a definition of the open set in topology. They are:
In point-set topology, the properties of the set S are:X and ∅ belongs to the set S.The intersection of any subsets belongs to the set S.The union of any subsets belongs to the set S.For instance:Let τ = {X,∅}. Then, it's the topology. We call that the trivial or discrete topology. If the set is indiscrete topology, then it contains infinitely many elements!
In the standard topology on the rational numbers ( \mathbb{Q} ), a singleton set ( {q} ) is not open because you cannot find a rational interval around ( q ) that contains only ( q ) and no other points from ( \mathbb{Q} ). In contrast, in the topology on the integers ( \mathbb{Z} ), which is discrete, every singleton set ( {z} ) is open because every integer is isolated from others, allowing us to form an open set containing just that integer. Therefore, singleton sets are open in ( \mathbb{Z} ) but not in ( \mathbb{Q} ).
The set of odd whole numbers is neither open nor closed in the context of standard topology on the real numbers. In topology, a set is considered closed if it contains all its limit points; however, odd whole numbers do not include any even numbers or fractions, which means they do not contain limit points that approach them. Additionally, they are not an open set because there are no neighborhoods around any of the odd whole numbers that entirely consist of odd whole numbers.
In the standard topology on (\mathbb{R}), a singleton set, such as ({a}), is not considered open. An open set is defined as one that contains a neighborhood around each of its points, meaning for any point (x) in the set, there exists an interval ((x - \epsilon, x + \epsilon)) that is entirely contained within the set. Since a singleton set contains only the point (a) and does not include any interval around it, it does not satisfy the criteria for being open in (\mathbb{R}).
Advantages include: Its easy to set up, handle, and implement, It is best-suited for small networks and its less costly. There 3 types of topology which are; ring, bus and star topology.
John D. Baum has written: 'Elements of point set topology' -- subject(s): Topology
In topology, there are various types, but the most commonly discussed include general topology (also known as point-set topology), algebraic topology, differential topology, and geometric topology. Each of these branches focuses on different aspects and properties of topological spaces. Additionally, there are many specific topological structures and concepts, such as metric spaces, homeomorphisms, and manifolds, which contribute to the richness of the field. Overall, the number of topologies can be considered vast and diverse, depending on the context in which they are studied.
There are three axioms that must be satisfied for a collection of subsets, t, of set B to be called a topology on B.1) Both B and the empty set, Ø, must be members of t.2) The intersection of any two members of t must also be a member of t.3) The union of any family of members of t must also be a member of t.If these axioms are met, the members of t are known as t-open or simply open, subsets of B.See related links.
Steven A. Gaal has written: 'Point set topology'
A star topology is best for a classroom environment. This topology is easy to set up and manage, and it allows for easy expansion of the network. Additionally, it is less susceptible to network outages due to a single point of failure.
A switch topology is an organizational representation of the channels and relays in a switch module. The topology establishes the default states for all relays in a module and defines the channel names. Some switches can use multiple topologies or variations of each topology type. Some terminal blocks or accessories may force the switch to use a given topology or set of topologies. GHOUL
A singleton set, such as {q} where q is a rational number, is not open in the space of rational numbers (Q) because any open interval around q will contain other rational numbers, thus making it impossible for {q} to be an open set. In contrast, in the space of integers (Z), singletons like {z} where z is an integer are considered open sets because the discrete topology on Z defines every subset as open. Therefore, in Z, each integer stands alone without any neighboring integers, allowing singletons to be open.