static L<Map<S, Lisp>> lispTruthMatches(Lisp pat, S... variables) {
  Set<S> vars = asSet(variables);
  new L<Map<S, Lisp>> out;
  for (LispStatement l : lispStatementsByHead(heads))
    addIfNotNull(out, lispMatch(pat, l.term, vars));
  ret out;
}