@Override
 public Frequency consumesInput(Language lang) {
   Frequency ff = lang.lali.consumesInput(first);
   switch (ff) {
     case NEVER:
       return lang.lali.consumesInput(second);
     case ALWAYS:
       return ff;
     case SOMETIMES:
       Frequency sf = lang.lali.consumesInput(second);
       switch (sf) {
         case ALWAYS:
         case SOMETIMES:
           return sf;
         case NEVER:
           return Frequency.SOMETIMES;
       }
       throw new AssertionError(sf.name());
   }
   throw new AssertionError(ff.name());
 }
 @Override
 public ImmutableRangeSet<Integer> lookahead(Language lang) {
   Frequency ff = lang.lali.consumesInput(first);
   switch (ff) {
     case NEVER:
       return lang.lali.lookahead(second);
     case ALWAYS:
       return lang.lali.lookahead(first);
     case SOMETIMES:
       TreeRangeSet<Integer> r = TreeRangeSet.create();
       r.addAll(lang.lali.lookahead(first));
       r.addAll(lang.lali.lookahead(second));
       return ImmutableRangeSet.copyOf(r);
   }
   throw new AssertionError(ff.name());
 }