“…Since then, a systematic study of the two-parameter quantum groups has been going on, see, for instance, ([BW2], [BW3]) for type A; ([BGH1], [BGH2]) for types B, C, D; [HS], [BH] for types G 2 , E 6 , E 7 , E 8 . For a unified definition, see ([HP1], [HP2]).…”