def curl(vect, coord_sys):
    """
    Returns the curl of a vector field computed wrt the base scalars
    of the given coordinate system.

    Parameters
    ==========

    vect : Vector
        The vector operand

    coord_sys : CoordSysCartesian
        The coordinate system to calculate the curl in

    Examples
    ========

    >>> R = CoordSysCartesian('R')
    >>> v1 = R.y*R.z*R.i + R.x*R.z*R.j + R.x*R.y*R.k
    >>> curl(v1, R)
    0
    >>> v2 = R.x*R.y*R.z*R.i
    >>> curl(v2, R)
    R.x*R.y*R.j + (-R.x*R.z)*R.k

    """
    return coord_sys.delop.cross(vect).doit()