loadPackage "Dmodules";
R=QQ[x_1,D_1, WeylAlgebra=>{x_1=>D_1}];
I = ideal(-(1-x_1)*(D_1*x_1-1)-1+4*x_1);
bFunction(I,{-1})
-- (-x_1 D_1 -4) (-x_1 D_1 -1)
-- =(-D_1 x_1 + 1 -4 )  (-D_1 x_1 +1 -1)