def vect3_cross(u, v):
    """
    Cross product.
    u, v (3-tuple): 3d vectors
    return (3-tuple): 3d vector
    """
    return (u[1] * v[2] - u[2] * v[1], 
            u[2] * v[0] - u[0] * v[2], 
            u[0] * v[1] - u[1] * v[0])