 The first case of algebraic "D"-modules are modules over the Weyl algebra "A""n"("K") over a field "K" of characteristic zero.It is the algebra consisting of polynomials in the following variables 
where the variables "x""i" and ∂"j" separately commute with each other, and "x""i" and ∂"j" commute for "i" ≠ "j", but the commutator satisfies the relation
For any polynomial "f"("x"1, ..., "x""n"), this implies the relation
thereby relating the Weyl algebra to differential equations.An (algebraic) "D"-module is, by definition, a left module over the ring "A""n"("K").