def check_col(x, y, digits_grid):
	"""
	Checks if a digit in a box with coordinates y, x fits to its column.
	Useful for checking if sudoku is solvable at all.

	:param x:
		a coordinate counted from 0
	:param y:
		a coordinate counted from 0
	:param digits_grid:
		2D numpy array that contains digits. 0 <==> there is no digit, blank box
	:return:
		True or False
	"""
	for i in range(9):
		if i != y and digits_grid[i, x] == digits_grid[y, x]:
			return False
	return True