def chiffre_barre_colonne(s, r, j):
    """
    Look into every number in column *j*,
    if the number in column *k* ``s[i][k]`` is not null,

    @param      s       current state of the sudoku
    @param      r       array ``r[n] == 0`` means number *n+1* is already taken on this column
    @param      j       column index (0 based)
    """
    for k in range(0, 9):
        if s[k][j] > 0:
            r[s[k][j] - 1] = 0
