backProp score winner z
  | (maxPlayers (treeState (zipperTree z))) == 1 = backPropHelper1 score z
  | (isDraw (outcome (treeState (zipperTree z)))) = backPropHelper1 score z
  | (isWin (outcome (treeState (zipperTree z)))) = backPropHelperMany score winner z
  | otherwise = (goToParent z)