bool includes(const Name& name) const { return constant() != NULL && *constant() == name;
bool includes(const Variable& var, size_t step_id) const { for (const VariableChain* vc = cd_set(); vc != NULL; vc = vc->tail) { if (*vc->head.first == var && vc->head.second == step_id) { return true; } } return false;
  bool includes(const Name& name) const {    return constant() != NULL && *constant() == name;  }