countable

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countable

[′kau̇nt·ə·bəl]
(mathematics)
Either finite or denumerable. Also known as enumerable.

countable

(mathematics)
A term describing a set which is isomorphic to a subet of the natural numbers. A countable set has "countably many" elements. If the isomorphism is stated explicitly then the set is called "a counted set" or "an enumeration".

Examples of countable sets are any finite set, the natural numbers, integers, and rational numbers. The real numbers and complex numbers are not
References in periodicals archive ?
n])(x)}, orthogonal on a countable set of points, and they correspond to a determinate moment problem or to an indeterminate moment problem and the orthogonality measure is extremal, then one can find the corresponding orthogonality measure for dual set of polynomials, if they exist.
Since the spectrum of the operator A is discrete, only a countable set of these functions belongs to the Hilbert space H.
In particular, we show how one can naturally interpret the duality of families of polynomials, orthogonal on countable sets of points.
In section 2, we also discuss how one can naturally extend the conventional notion of duality to sets of polynomials, orthogonal on countable sets of points.
When one considers dual sets of q-polynomials, orthogonal on countable sets of points, then one member of these sets corresponds to the determinate moment problem and another to the indeterminate moment problem.
It is not obvious how to extend the notion of duality to polynomials, orthogonal on countable sets of points.