Superposition in the $p$-Laplace Equation
  That a superposition of fundamental solutions to the $p$-Laplace Equation is $p$-superharmonic -- even in the non-linear cases $p>2$ -- has been known since M. Crandall and J. Zhang published their paper "Another Way to Say Harmonic" in 2003. We give a simple proof and extend the result by means of an explicit formula for the $p$-Laplacian of the superposition. 
Karl K. Brustad
math.AP