Convex PBW-type Lyndon basis and restricted two-parameter quantum groups of typeG2

Abstract

From the 2-parameter quantum group Ur,s(G2) defined by Hu and Shi in 2007, we construct finite-dimensional pointed Hopf algebras ur,s(G2) (that is, restricted 2-parameter quantum groups); these turn out to be Drinfel�d doubles. Crucial is a detailed combinatorial construction of the convex PBW-type Lyndon basis for type G2 in the 2-parameter quantum version. We exhibit the possible commutation relations among quantum root vectors. Then we show that the restricted quantum groups are ribbon Hopf algebras under certain conditions, by determining their left and right integrals. We also determine all the Hopf algebra isomorphisms of ur,s(G2) by describing its sets of left (right) skew-primitive elements.