“…In recent years numerous works have been dedicated to the calculus of variations on time scales and their generalizations -see [7,12,13,18,21,22,23,24,26] and the references therein. Most of them deal with delta or nabla derivatives of first-order [2,3,4,5,6,9,11,16,19,20], only a few with higher-order derivatives [10,25].…”