Infinitesimals could not be found for the given ODE

Raise code

 hint == 'default':
                for heuristic in lie_heuristics:
                    function = globals()['lie_heuristic_' + heuristic]
                    xieta = function(match, comp=False)
                    if xieta:
                        return xieta

                raise NotImplementedError("Infinitesimals could not be found for"
                    " the given ODE")

            elif hint not in lie_heuristics:
                 raise ValueError("Heuristic not recognized: " + hint)

            else:
                 function = globals()['lie_heuristic_' + hint]