Clone (algebra)
In the area of mathematics known as universal algebra, a clone is a set C of finitary operations on a set A such that C contains all the projections πkn: An → A, defined by πkn(x1, …, xn) = xk, C is closed under (finitary multiple) composition (or "superposition"): if f, g1, …, gm are members of C such that f is m-ary, and gj is n-ary for all j, then the n-ary operation h(x1, …, xn) := f(g1(x1, …, xn), …, gm(x1, …, xn)) is in C. The question whether clones should contain nullary operations or not is not treated uniformly in the literature. The classical approach as evidenced by the standard monographs on clone theory considers clones only containing at-least-unary operations.