form-as well as (1.4). The boundary condition at infinity imposed by (1.4) is taken account of by the relations U ∈ L 6 (Ω c) 3 , ∇U ∈ L 2 (Ω c) 9. (We refer to Section 2 for the definition of our function spaces and for other notation.) Leray solutions to (1.3), (1.4) exist under suitable assumptions on F and ∂Ω. More details may be found in [23, Theorem VII.2.1, II.5.1]. If F decays sufficiently fast, it may be shown that U ∈ L p (Ω c) 3 for p ∈ (2, ∞] and ∇U ∈ L p (Ω c) 9 for p ∈ (4/3, ∞] ([24, Theorem X.4.1]). In the work at hand, it is sufficient to suppose U ∈ L p (Ω c) 3 for p ∈ (2, ∞) and ∇U ∈ L p (Ω c) 9 for p ∈ (4/3, 3+ 0 ], with some 0 > 0. Then U ∈ W 1, 3+ 0 (Ω c) 3 , so U ∈ L ∞ (Ω c) 3 by a Sobolev inequality, and also |U (x)| → 0 for |x| → ∞, as explained in [12, p. 209]. Therefore the assumptions U ∈ L p (Ω c) 3 for p ∈ (2, ∞) and ∇U ∈ L p (Ω c) 9 for p ∈ (4/3, 3 + 0 ] mean in particular that U ∈ L p (Ω c) 3 for p ∈ (2, ∞], |U (x)| → 0 for |x| → ∞, (1.4) ∇U ∈ L p (Ω c) 9 for p ∈ (4/3, 3]. These are the properties of U we will actually use in what follows. We are interested in conditions which guarantee asymptotic stability of U , that is, if U ∈ W 1,2 0 (Ω c) 3 ∩ H 2 (Ω c), and if the quantity U − U 2 + ∇(U − U 2 is sufficiently small, then the velocity part v of a solution (v, π) of the initial-boundary value problem Proof: We proceed as in [23, p. 177-178]. Take R and V as in the lemma. First suppose that q < 3. Then Hölder's inequality yields V |B 2R \B R q ≤ C R V |B c R 3q/(3−q). On the other hand, a scaling argument and Theorem 3.4 with A = B R 0 imply V |B c R 3q/(3−q) = (R/R 0) (3−q)/q V (R/R 0) • |B R 0 c 3q/(3−q)