anchor.diff:    static Set<BoardLoc> _dykstraConnections(Board board, Set<BoardLoc> seen, Set<BoardLoc> fringe){
       //if fringe is empty, return
       if(fringe.length == 0) return seen;
  +    
  +    //else remove first fringe, add it to seen, add neighbors to fringe, and recurse
       var first = fringe.first;
       fringe.remove(first);
       seen.add(first);
  
positive.code:   }
    
    bool validPaymentPath (BoardLoc loc, Card card, CardDirection playedDir, int playerNum, PaymentPath path){
      if (path == null || path.length < 2) => false;
      
      //validate connection to start of path
      bool connectsToPath = CardUtil.allDirections.any((dir) =>
  
negative.code:   }
  
    bool pathIsConnected(PaymentPath path) {
      if(path.length < 2) return true;
      //(first, rest)
      BoardLoc first = path.removeAt(0);
      
  