  We investigate second order elliptic equations \[F(\mathcal{H}u) = 0\] where
the function $F\colon S(n)\to\mathbb{R}$ on the space of symmetric $n\times n$
matrices is assumed to be sublinear.
  There is very little to be found in the literature devoted particularly to
sublinear elliptic operators. When examples of such operators occur, they are
often merely treated as members of the larger class of convex operators. That
class has been thoroughly investigated and many of its aspects are well
understood.
  There is, however, something to be said about sublinear operators that do
not, in general, apply to convex operators.
