A rapid proof for a flattening property of a classical solution of the Mullins equation

Modifying previous proof based on the maximum principles [J. Math. Phys. 27, 1391 (1986); 28, 536, 2982 (1987)], a rapid proof is proposed for a flattening property of a classical solution of the Cauchy problem associated with the Mullins equation ut=uxx/(1+ux2), (x,t)∈R1×(0,∞), u(x,0)=α(x), x∈R1 which describes the development of material surface due to evaporation condensation.