On theq-Commutations inUq( ) at Roots of One

Let be a root of one and a semisimple Lie algebra with triangular decomposition = + + − . LetU + (resp.Ures + ) be the nonrestricted (resp. restricted) quantum enveloping algebra of . We prove that Fract U + is a quantum Weyl field. We then give a description of the -center ofU + . LetUfin + be the finite part ofUres + . Via the Drinfeld correspondence, theUfin + -covariant space of a Weyl module is -central. In case = n, this enables us to describe this space in terms of semistandard Young tableaux.