On the Harnack inequality for quasilinear elliptic equations with a   first order term
  We consider weak solutions to $$-\Delta_pu+a(x,u)|\nabla u|^q=f(x,u),$$ with $p>1$, $q\geq\max\,\{p-1,1\}$. We exploit the Moser iteration technique to prove a Harnack comparison inequality for $C^1$ weak solutions. As a consequence we deduce a strong comparison principle. 
Susana Merch\'an, Luigi Montoro, Bernardino Sciunzi
math.AP