I know the definition of convolution product in D.Gaitsgory's paper, but I can give a convolution product
$p:G(K)\times Fl \to Fl\times Fl$,$q:G(K)\times Fl \to G(K)\times_{G(O)} Fl$, $m:G(K)\times_{G(O)} Fl \to Fl$
$A_1,A_2\in P_I (Fl)$,$A_1*A_2=Rm^* A$ ,$q^* A=p^*(A_1\times A_2)$
Does this definition coincide with the Gaitsgory's sense?