When are two Coxeter orbifolds diffeomorphic?

One can define what it means for a compact manifold with corners to be a "contractible manifold with contractible faces."Two combinatorially equivalent, contractible manifolds with contractible faces are diffeomorphic if and only if their four-dimensional faces are diffeomorphic.It follows that two simple convex polytopes are combinatorially equivalent if and only if they are diffeomorphic as manifolds with corners.On the other hand, by a result of Akbulut, for each n ≥ 4, there are smooth, contractible n-manifolds with contractible faces that are combinatorially equivalent but not diffeomorphic.Applications are given to rigidity questions for reflection groups and smooth torus actions.