parameter (pair (list string) (list string));
storage unit;
return bool;
code {CAR; DUP; CAR; DIP{CDR}; EMPTY_SET string; SWAP;
      LAMBDA (pair string (set string)) (set string) {DUP; CAR; DIP{CDR}; PUSH bool True; SWAP; UPDATE};
      REDUCE; PUSH bool True; SWAP; PAIR; SWAP;
      LAMBDA (pair string (pair (set string) bool))
             (pair (set string) bool)
             {DUP; DUP; CAR; DIP{CDAR; DIP{CDDR}; DUP}; MEM; DIP{SWAP}; AND; SWAP; PAIR};
      REDUCE; CDR; UNIT; SWAP; PAIR};
