Given a function φ and s ∈ (0, 1), we will study the solutions of the following obstacle problem:
u ≥ φ in ℝn,
(−▵)su ≥ 0 in ℝn,
(−▵)su(x) = 0 for those x such that u(x) > φ(x),
lim|x| → + ∞ u(x) = 0.
We show that when φ is C1, s or smoother, the solution u is in the space C1, α for
every α < s. In the case where the contact set {u = φ} is convex, we prove the
optimal regularity result u ∈ C1, s. When φ is only C1, β for a β < s, we prove
that our solution u is C1, α for every α < β. © 2006 Wiley Periodicals, Inc.