In topology, a branch of mathematics, a first-countable space is a topological space satisfying the "first axiom of countability". Specifically, a space X is said to be first-countable if each point has a countable neighbourhood basis (local base). That is, for each point x in X there exists a sequence U1, U2, … of open neighbourhoods of x such that for any open neighbourhood V of x there exists an integer i with Ui contained in V.
Read more about First-countable Space: Examples and Counterexamples, Properties
Famous quotes containing the word space:
“I would have broke mine eye-strings, cracked them, but
To look upon him, till the diminution
Of space had pointed him sharp as my needle;
Nay, followed him till he had melted from
The smallness of a gnat to air, and then
Have turned mine eye and wept.”
—William Shakespeare (1564–1616)