  We deal with non negative functions satisfying \[ \left\{ \begin{array}{ll}
(-\Delta)^s u_s=0 & \mathrm{in}\quad C, u_s=0 & \mathrm{in}\quad
\mathbb{R}^n\setminus C, \end{array}\right. \] where $s\in(0,1)$ and $C$ is a
given cone on $\mathbb R^n$ with vertex at zero. We consider the case when $s$
approaches $1$, wondering whether solutions of the problem do converge to
harmonic functions in the same cone or not. Surprisingly, the answer will
depend on the opening of the cone through an auxiliary eigenvalue problem on
the upper half sphere. These conic functions are involved in the study of the
nodal regions in the case of optimal partitions and other free boundary
problems and play a crucial role in the extension of the
Alt-Caffarelli-Friedman monotonicity formula to the case of fractional
diffusions.
