On a principle of reciprocity between high- and low-frequency problems concerning linear differential equations of second order
form a polynomial basis for polynomials in the components of n vectors u\r) which are linear in each of the vectors and form-invariant under the transformations associated with transverse isotropy about the x3 axis. As in the previous sections, we immediately see that a basic set of anisotropic tensors for transverse isotropy about the x3 axis is defined by du{3r) /du\r) (= a4 , say) and d(u[r) u^/diii'* duj'* (= /3,,) (r 7* s; a = 1, 2; i,j = 1, 2, 3). We obtain immediately