I keep getting invalid set index error, what should I do?

Question

Hi, I am writing a minmax code for a game, but whenever I run it I get the error Invalid set index 'start' (on base: 'Node (main.gd)') with value of type 'bool'. What does it mean and how do I fix it.

extends Node
var board=[7,5,3,1]
func _ready():
    self.board=board
    self.start=true
    makechilds(self)
func makechilds(pnode):
    for x in range(0,4):
        board=pnode.board
        for y in range (0,pnode.board[x]):
            board[x]-=1
            var child=Node
            child.board=board
            child.done=false
            child.start=false
    pnode.done=true
    nextsubject(pnode)
func nextsubject(pnode):
    for i in range (0,pnode.get_child_count( )):
        if not pnode.get_child(i).board==[0,0,0,0] and pnode.get_child(i).done==false:
            makechilds(pnode.get_child(i))
    if pnode.start==false:
        nextsubject(pnode.get_parent())
    else:
        print('done')

Answer 1

Because You never introduce variable "start" anywhere !

It must exist before You set it in ready function. Do the same thing You did with "board" variable : introduce it with VAR keyword