Elliptic root systems of type $A_۱$, a combinatorial study

We consider some combinatorics of elliptic root systems of type $A_۱$. In particular, with respect to a fixed reflectable base, we give a precise description of the positive roots in terms of a ``positivity'' theorem. Also the set of reduced words of the corresponding Weyl group is precisely described. These then lead to a new characterization of the core of the corresponding Lie algebra, namely we show that the core is generated by positive root spaces.

Keywords:

Elliptic root systems , Elliptic Lie algebras , Jordan algebras