A topology is given by a collection of subsets of a topological space 
.
The smallest topology has two open sets, the empty
set 
and 
.
The largest topology contains all subsets as open sets, and is called the discrete
topology. In particular, every point in 
is an open set in the discrete
topology.
Discrete Topology
See also
Discrete Mathematics, Discrete Set, Topological SpaceThis entry contributed by Todd Rowland
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Rowland, Todd. "Discrete Topology." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/DiscreteTopology.html