sclass Relation {
  S relation;
  L<S> things;
  
  *() {}
  *(S *relation, L<S> *things) {}
  *(S *relation, S... things) { this.things = asList(things); }
  
  bool is(S s) { ret eqic(relation, s); }
  S get(int i) { ret get(things, i); }
  
  [stdEq]
}