  Generalizing the well-known mean-value property of harmonic functions, we
prove that a p-harmonic function of two variables satisfies, in a viscosity
sense, two asymptotic formulas involving its local statistics. Moreover, we
show that these asymptotic formulas characterize p-harmonic functions when 1 <
p < \infty. An example demonstrates that, in general, these formulas do not
hold in a non-asymptotic sense.
