The F and B matrices associated with Virasoro null vectors are derived
in closed form by making use of the operator-approach suggested by th
e Liouville theory. It is found that the entries of the fusing and bra
iding matrices are not simply equal to quantum-group symbols, but invo
lve additional coupling constants. Their derivation neatly follows fro
m the differential equations which express the decoupling of Virasoro
null vectors, combined with the general scheme of Moore and Seiberg. T
he present operator formalism, contrary to the Coulomb-gas approach, a
llows to study the coefficients of the operator-product algebra to all
orders. Altogether the present work, and a subsequent article, give t
he concrete realization of Moore and Seiberg's scheme that describes t
he chiral operator-algebra of two-dimensional gravity and minimal mode
ls.