def manhatten(a: tuple, b: tuple):
	"""
	Manhattan distance
	The standard heuristic for a square grid.

	:param a: tuple  Start node position
	:param b: tuple  End node position
	:return: float
	"""
	ax, ay, bx, by = a[0], a[1], b[0], b[1]
	dx = abs(ax - bx)
	dy = abs(ay - by)
	return dx + dy