 An abstract CR structure on a real manifold "M" of real dimension "n" consists of a complex subbundle "L" of the complexified tangent bundle which is formally integrable, in the sense that ["L","L"] ⊂ "L", which has zero intersection with its complex conjugate.The CR codimension of the CR structure is formula_39 where dim "L" is the complex dimension.In case "k" = 1, the CR structure is said to be of hypersurface type.