Derivatives for equational theories

In recent papers by Kearnes&Szendrei and by Freese, several different notions of "derivative" for idempotent equational theories have been defined. Each of those different derivatives is obtained by adding some new identities to the theory. These notions of derivative turn out to be closely related to important Maltsev type conditions like congruence modularity and n-permutability. In this seminar we will introduce these notions and results.