We show that an infinity harmonic function, that is, a viscosity solution of the nonlinear PDE − ∞ u = −u x i u x j u x i x j = 0, is everywhere differentiable. Our new innovation is proving the uniqueness of appropriately rescaled blow-up limits around an arbitrary point.
Mathematics Subject Classification (2000)Primary 49N60 · Secondary 35J20 · 35J65