  Adapting the method of Andrews-Clutterbuck we prove an eigenvalue gap theorem
for a class of non symmetric second order linear elliptic operators on a convex
domain in euclidean space. The class of operators includes the Bakry-Emery
laplacian with potential and any operator with second order term the laplacian
whose first order terms have coefficients with compact support in the open
domain. The eigenvalue gap is bounded below by the gap of an associated
Sturm-Liouville problem on a closed interval.
