Fort Space

In mathematics, Fort space, named after M. K. Fort, Jr., is an example in the theory of topological spaces.

Let X be an infinite set of points, of which P is one. Then a Fort space is defined by X together with all subsets A such that:

  • A excludes P, or
  • A contains all but a finite number of the points of X

X is homeomorphic to the one-point compactification of a discrete space.

Modified Fort space is similar but has two particular points P and Q. So a subset is declared "open" if:

  • A excludes P and Q, or
  • A contains all but a finite number of the points of X

Fortissimo space is defined as follows. Let X be an uncountable set of points, of which P is one. A subset A is declared "open" if:

  • A excludes P, or
  • A contains all but a countable set of the points of X

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