def rotation_constraint(normal):
    """
    Given a normal defining a plane, return the axis of rotation allowed by this constraint.
    """
    # Normalize the normal vector
    normal = np.array(normal)
    normalized_normal = normal / np.linalg.norm(normal)

    return normalized_normal

    Given a normal defining a plane, return the axis of rotation allowed by this constraint.
    
infinigen/core/constraints/example_solver/geometry/dof.py