A. Albert, "Structure of algebras", Colloquium publications 24, American Mathematical Society, 2003, ISBN 0-8218-1024-3. ###>As congruences on rings are characterized by their ideals, this notion is a straightforward generalization of the notion from ring theory: a ring is simple in the sense that it has no nontrivial ideals if and only if it is simple in the sense of universal algebra.