a wide class of equivalence problems can be formulated in the language of "g"-structures. for example, a pair of riemannian manifolds are (locally) equivalent if and only if their bundles of orthonormal frames are (locally) isomorphic "g"-structures. in this view, the general procedure for solving an equivalence problem is to construct a system of invariants for the "g"-structure which are then sufficient to determine whether a pair of "g"-structures are locally isomorphic or not.