of the equation's degeneracy law satisfies an integrability criterium, viz. σ− 1∈ L 1 (1 λ d λ).
The proof is based upon the construction of a sequence of converging tangent hyperplanes
that approximate u (x), near x 0, by an error of order o (| x− x 0|). Explicit control of such
hyperplanes is carried over through the construction, yielding universal estimates upon the
C 1–regularity of solutions. Among the main new ingredients required in the proof, we …