func: function exit(bytes32 _listingHash) external {
          Listing storage listing = listings[_listingHash];
  
          require(msg.sender == listing.owner);
          require(isWhitelisted(_listingHash));
  
          
          require(listing.challengeID == 0 || challenges[listing.challengeID].resolved);
  
          
          resetListing(_listingHash);
          _ListingWithdrawn(_listingHash);
      }