Abstract:
We expose fundamentals of the theory of varieties of nilpotent $\mathrm{MR}$-groups and compare various definitions of nilpotency in this category.
Keywords:Lyndon $\mathrm R$-group, Hall $\mathrm R$-group, $\mathrm{MR}$-group, variety of $\mathrm{MR}$-groups, $\alpha$-commutator, tensor completion, nilpotent $\mathrm{MR}$-group.