static L<TripleRef<S>> ai_thoughtSpace_query(S a, S b, S c, AbstractThoughtSpace ts) {
  l = null;
  if (!isDollarVar(a)) l = shortestList(l, ts.get(a));
  if (!isDollarVar(b)) l = shortestList(l, ts.get(b));
  if (!isDollarVar(c)) l = shortestList(l, ts.get(c));
  ret l;
}