# Construct a state form `initial_grid`
	redef fun initial_state do
		var g = initial_grid
		var len = g.length
		var width = len.sqrt.to_i
		self.width = width
		if width * width != len then
			print "Error: {g} has {len} tiles. A square number, like {width*width} is needed"
			exit 1
		end
		var res = new ArrayCmp[Tile]
		for i in [0..g.length[ do
			var c = g.chars[i]
			if c == ' ' or c == '.' then
				var hole = new Tile('.', -1)
				self.hole = hole
				res.add hole
			else if c >= '1' and c <= '9' then
				var t = new Tile(c, '1'.distance(c))
				res.add t
			else if c >= 'a' and c <= 'z' then
				var t = new Tile(c, 'a'.distance(c))
				res.add t
			else if c >= 'A' and c <= 'Z' then
				var t = new Tile(c, 'A'.distance(c))
				res.add t
			else
				print "Error: illegal tile {c} in {g}"
				exit 1
			end
		end
		return res
	end