def check_if_points_escape_box(u, box_boundaries):
    """
    Determine if points u in 2D plane have escaped from box_boundaries limits.
    
    Parameters
    ----------
    u : ndarray, shape(n, 2),
        Points in plane.
    
    box_boundaries : list of 2 tuples of floats,
        Values are interpreted as [[x_min,x_max], [y_min, y_max]].
        
    Returns
    -------
    u_indices : ndarray of bools, shape(n, 2),
        True/False for points inside/outside the box_boundaries respectively.
    """
    x, y = u.T
    # Escape condition
    box_x_min, box_x_max = box_boundaries[0]
    box_y_min, box_y_max = box_boundaries[1]
    u_indices = (x >= box_x_min) & (x <= box_x_max) & (y >= box_y_min) & (y <= box_y_max)
    return u_indices