Comment on: I-Shih Liu: Constitutive theory of anisotropic rigid heat   conductors
  In I-Shih Liu's paper \C{1}, the compatibility of anisotropy and material frame indifference of a rigid heat conductor is investigated. For this purpose, the deformation gradient is introduced into the domain of the constitutive mapping. Because of the presupposed rigidity, the deformation gradient is here represented by an orthogonal tensor. The statement, that the usual procedure -- not to introduce the deformation gradient into the state space of rigid heat conductors -- causes isotropy because of the material frame indifference, is misleading. 
Wolfgang Muschik
math-ph math.MP