 Let formula_34 be the subbundle of vectors annihilating all of the defining functions formula_35 Note that, by the usual considerations for integrable distributions on hypersurfaces, "L" is involutive.Moreover, the independence condition implies that "L" is a bundle of constant rank "n" − "k".Henceforth, suppose that "k" = 1 (so that the CR manifold is of hypersurface type), unless otherwise noted.