LAUSR

Abstract Let θ be an inner function on the unit disk, and let K θ p : = H p ∩ θ H 0 p ‾ be the associated star-invariant subspace of the Hardy space H p , with p ≥ 1 . While a nontrivial function f ∈ K θ p is never divisible by θ, it may have a factor h which is ‘‘not too different” from θ in the sense that the ratio h / θ (or just the anti-analytic part thereof) is smooth on the circle. In this case, f is shown to have additional integrability and/or smoothness properties, much in the spirit of the Hardy–Littlewood–Sobolev embedding theorem. The appropriate norm estimates are established, and their sharpness is discussed.