“…While the invariants tr(CL i ), i = 0, 1, ..., n, and trC 3 are convex with respect to F, the terms tr(C 2 L i ), i = 1, 2, ..., n, are not. However, they can be expressed in terms of convex invariants with respect to F, adjF and detF [1,5] which leads to the alternative representation of the strain energy…”