Lie symmetry of a class of nonlinear boundary value problems with free   boundaries
  A class of (1+1)--dimensional nonlinear boundary value problems (BVPs), modeling the process of melting and evaporation of solid materials, is studied by means of the classical Lie symmetry method. New definition of invariance in Lie's sense for BVP is presented and applied for the class of BVPs in question. 
Roman Cherniha and Sergii Kovalenko
math-ph math.MP