static Map<S, MultiSet<S>> ai_gazelle_indexStatementsByRule_multiSet(MultiSet<S> statements) {
  new Map<S, MultiSet<S>> map;
  new Matches m;
  for (S s : keys(statements))
    if "Rule *: ..." {
      S ruleID = $1;
      getOrCreateMultiSet(map, ruleID).add(m.rest(), statements.get(s));
    }
  ret map;
}

Began life as a copy of #1021444