Mekso unary or binary operator: n-set or integer interval; in unary form, it maps a nonnegative integer X_{1 }= n to the set \1, \dots , n\ (fully, officially, and precisely: the intersection of (a) the set of exactly all positive integers with (b) the closed ordered interval [1, n] such that n \geq 1; see notes for other n); in binary form, it maps ordered inputs (X_{1, X}= (m, n) to the intersection of (a) the set of exactly all integers with (b) the closed ordered interval [m, n].

0 on its own induces the unary form of this word and thus maps to the empty set ∅. Inputting infinity (for the unary form) produces the set of exactly all positive integers (sometimes also onown as: natural numbers), Z^{+ }= N. The upper bound is always specified; when the lower bound is not specified, it defaults to 1 and the upper bound must equal or exceed 1 (else the output is ∅). If this word is represented by f, and Z represents the set of exactly all integers, and (n, m \in Z \cup Set(\pm \infty): m \leq n), then: f(m, n) = Z \cap [m, n], and furthermore: if 1 \leq n, then f(n) = f(1, n) = Z \cap [1, n], else f(n) = ∅. The definition extends naturally (and with only trivial modification) to non-integer real-valued n, m, but it is recommended to keep them as integers when possible. Z excludes \pm \infty.