Groups and Lie algebras corresponding to the Yang–Baxter equations

For a positive integer n we introduce quadratic Lie algebras trn, qtrn and finitely discrete groups Trn, QTrn naturally associated with the classical and quantum Yang–Baxter equation, respectively.We prove that the universal enveloping algebras of the Lie algebras trn, qtrn are Koszul, and compute their Hilbert series. We also compute the cohomology rings for these Lie algebras (which by Koszulity are the quadratic duals of the enveloping algebras). Finally, we construct a basis of U(trn).We construct cell complexes which are classifying spaces of the groups Trn and QTrn, and show that the boundary maps in them are zero, which allows us to compute the integral cohomology of these groups.We show that the Lie algebras trn, qtrn map onto the associated graded algebras of the Malcev Lie algebras of the groups Trn, QTrn, respectively. In the case of Trn, we use quantization theory of Lie bialgebras to show that this map is actually an isomorphism. At the same time, we show that the groups Trn and QTrn are not formal for n⩾4.