def peers(row: Int, col: Int): List[(Int, Int)] = {
    val rowStart = (row % 3) match {
      case 0 => row
      case 1 => row-1
      case 2 => row-2
    }
    val colStart = (col % 3) match {
      case 0 => col
      case 1 => col-1
      case 2 => col-2
    }

    val box = (for (i <- rowStart to rowStart + 2 ; j <- colStart to colStart + 2)
      yield (i, j)).toList

    val unfiltered =
    ((for (i <- 0 to 8) yield (row, i)) ++ (for (j <- 0 to 8) yield (j, col))++ box).toList

    (unfiltered filter (x => x != (row, col))).toSet.toList //removes duplicates
  }
}