Universal extensions

作者：Peschke George^*

来源：Comptes Rendus Mathematique, 2011, 349(9-10): 501-504.

DOI：10.1016/j.crma.2011.04.009

In the category of left modules over a unital ring we show that a left exact reflector determines, for each n >= 1, a torsion theoretic setting in which universal extensions of length n exist. Combined with recent work of Rodelo and van der Linden (2011) [9] this establishes the existence of universal central extensions of groups and Lie algebras. Interpreted in the homotopy category of topological spaces, it provides a new perspective on existing results about Quillen's plus construction and its effect on homotopy groups.

• 出版日期2011-5