  We prove that the fractional derivatives of solutions to a class of nonlocal
fully nonlinear elliptic equations are epsilon-integrable. We follow Fanghua
Lin's original approach to the analogous problem for second order equations, by
first proving a potential estimate, then combining this estimate with the
ABP-type estimate by N. Guillen and R. Schwab to control the size of the
superlevel sets of the fractional derivatives of solutions.
