Space S000057

Rational sequence topology

For each irrational xRx \in \mathbb{R} fix a sequence of rational numbers xixx_i \rightarrow x. The rational sequence topology on R\mathbb{R} is defined by declaring each rational point open and letting Un(x)={xi:i>n}{x}U_n(x) = \{x_i : i>n\} \cup \{x\} be a local basis at each irrational xx.

Note that in MathOverflow 447593 it was shown there are 2c2^{\mathfrak c} distinct topologies defined in this way, depending on the choices made for xix_i. However, none of the properties currently tracked for this space rely on this information.

Defined as counterexample #65 ("Rational Sequence Topology") in DOI 10.1007/978-1-4612-6290-9.

S57: Rational sequence topology | π-Base