oint([rho, 0])
    >>> fx, fy = R2_r.base_scalars()
    >>> ftheta = BaseScalarField(R2_r, 1)

    >>> fx(point)
    rho
    >>> fy(point)
    0

    >>> (fx**2+fy**2).rcall(point)
    rho**2

    >>> g = Function('g')
    >>> fg = g(ftheta-pi)
    >>> fg.rcall(point)
    g(-pi)

    Tc