
 Application, f(x), of a function, f, to an actual parameter, x.
May also be written as f x,
or as postfix, x f,
or even as x^{f}.
Also see composition.
 Associative, where a binary operation, '·', satisfies
(a · b) · c = a · (b · c),
e.g., addition (+) of integers
(but not subtraction ()).
 Commutative, where a binary operation, '·', satisfies
a · b = b · a, for all appropriate a and b,
e.g., addition (+) of integers.
 Composition, f·g, of functions g:X→Y and f:Y→Z,
(f·g)(x) = f(g(x)), f·g:X→Z;
apply g first and then f.
Note that composition is associative,
(f·g)·h = f·(g·h).
(f·g is sometimes written as fg,
and sometimes as postfix g;f, or even gf!)
Also see application.
 Graph, see [here].
 Group, see [here].
 iff, short for "if and only if," ⇔.
 s.t., short for "such that".

 N, the natural numbers, {0, 1, 2, 3, ... }.
 Q, the rational numbers, {m/n  m∈Z, n∈N{0}}.
 R, the real numbers. (Can't enumerate them!)
 S_{n}, the symmetric group
(of permutations) over {1,...,n}.
 Z, the integers, { ..., 2, 1, 0, 1, 2, 3, ... }.
 Z_{n}, the integers modulo (mod) n,
{0, 1, ..., n1}.
 Z_{p}, as above, {0, 1, ..., p1},
where p is a prime number.

 ∀, for all; also see
[logic] and
[spec.chars].
 ∃, there exists.
 ∧, as in p∧q, p and q, conjunction.
 ∨, as in p∨q, p or q, disjunction.
 ¬, as in ¬p, not p, logical negation.
 ∈, as in x∈S, x is a member of S.
 ∩, as in S∩T, set intersection.
 ∪, as in S∪T, set union.
 x, the size of x, the length of a sequence or string,
the number of elements in a set, etc..
 [y,z] = {x  y ≤ x ≤ z}, closed interval.
 [y,z) = {x  y ≤ x < z}, half closed interval.
 (y,z] = {x  y < x ≤ z}, half closed interval.
 (y,z) = {x  y < x < z}, open interval
(but also unordered pair in other contexts).
 ⟨x, y⟩, ordered pair,
note ⟨x, y⟩ ≠ ⟨y, x⟩ in general.

 {x  p(x)}, the set of x such that p(x) is true.

