parameter (pair (set string) (set string));
return bool;
storage unit;
code { CAR; DUP; CDR; DIP{CAR}; # Unpack lists
       PUSH bool True;
       PAIR; SWAP;              # Setup accumulator
       LAMBDA (pair string (pair bool (set string)))
              (pair bool (set string))
              { DUP;            # Unpack accumulator and input
                CAR;
                DIP{ CDR; DUP; DUP; CDR;
                     DIP{CAR; DIP{CDR}}};
                MEM;            # Check membership
                AND;            # Combine accumulator and input
                PAIR};
       REDUCE;                  # Reduce
       CAR;                     # Get the accumulator value
       UNIT; SWAP; PAIR}        # Calling convention
