This modern understanding uses algebra, in particular, universal algebra. For Schaefer's dichotomy theorem, the most important concept in universal algebra is that of a polymorphism. An operation formula_5 is a polymorphism of a relation formula_6 if, for any choice of "m" tuples formula_7 from "R", it holds that the tuple obtained from these "m" tuples by applying "f" coordinate-wise, i.e. formula_8, is in "R". That is, an operation "f" is a polymorphism of "R" if "R" is closed under "f": applying "f" to any tuples in "R" yields another tuple inside "R". A set of relations Γ is said to have a polymorphism "f" if every relation in Γ has "f" as a polymorphism. This definition allows for the algebraic formulation of Schaefer's dichotomy theorem.