Setting the "vertex_invariant" parameter to the isomorphism function does not seem to have any affect on the behavior of the function. In isomorphism.hpp, it appears that the function "isomorphism_impl" is supposed to read the parameter at the return statement: return isomorphism(G1, G2, f, choose_param(get_param(params, vertex_invariant1_t()), invariant1), choose_param(get_param(params, vertex_invariant2_t()), invariant2), choose_param(get_param(params, vertex_max_invariant_t()), ( invariant2.max )()), index_map1, index_map2 ); If "vertex_invariant1_t()" and "vertex_invariant2_t()" are both changed to "vertex_invariant_t()", the setting of the parameter then seems to have an affect. Has anyone been able to successfully set the vertex_invariant parameter using the named parameter version of the isomorphism function? I have had to resort to calling one of the internal isomorphism functions to set this parameter. any help is appreciated, Patrick