We now turn to the study of anisotropic material. It might be thought that the difficulties would be greatly enhanced but in fact, in the mathematical sense, the anisotropic is simpler than the isotropic case, the reason being that in the anisotropic case each term in the expression of the stress function is on the same footing whereas this is not so in the case of isotropy. Nevertheless the algebraic complexity of formulae is much greater. We might put the situation this way; in the anisotropic case formulae are obtained by simpler methods but are more complicated in algebraic structure.