Otherwise unconstrained; for example, the phrase ‘let x be an arbitrary real number’ introduces x as a real number, selected without constraint. The arbitrariness of the choice may only be implicit—let x ∈ ℝ—encapsulates the same. The term is commonly used to describe the constant of integration. The term might also be combined with constraints such as ‘let x be an arbitrary positive number’, so that, aside from being positive, x should be considered as any positive number.