The thesis deals with supernilpotence in loops, building on three equivalent definitions of higher commutators in Mal'tsev algebras due to Aichinger and Mud- rinski, Bulatov and Opršal. In the thesis, we study identities that occur in 1-, 2- and 3-supernilpotent loops. We prove that a k-supernilpotent loop has a k- nilpotent multiplication group. Moreover, we present results of our implementa- tion of algorithmic testing of supernilpotence in non-associative loops of small orders.

Title: Relational Approach to Universal Algebra Author: Jakub Opršal Department: Department of Algebra Supervisor: doc. Libor Barto, Ph.D., Department of Algebra Abstract: We give some descriptions of certain algebraic properties using rela- tions and relational structures. In the first part, we focus on Neumann's lattice of interpretability types of varieties. First, we prove a characterization of vari- eties defined by linear identities, and we prove that some conditions cannot be characterized by linear identities. Next, we provide a partial result on Taylor's modularity conjecture, and we discuss several related problems. Namely, we show that the interpretability join of two idempotent varieties that are not congruence modular is not congruence modular either, and the analogue for idempotent va- rieties with a cube term. In the second part, we give a relational description of higher commutator operators, which were introduced by Bulatov, in varieties with a Mal'cev term. Furthermore, we use this result to prove that for every algebra with a Mal'cev term there exists a largest clone containing the Mal'cev operation and having the same congruence lattice and the same higher commu- tator operators as the original algebra, and to describe explicit (though infinite) set of identities describing supernilpotence...