def plot(traj, x, y, **kwargs):
    """ Create a matplotlib plot of property x against property y

    Args:
        x,y (str): names of the properties
        **kwargs (dict): kwargs for :meth:`matplotlib.pylab.plot`

    Returns:
        List[matplotlib.lines.Lines2D]: the lines that were plotted

    """
    from matplotlib import pylab
    xl = yl = None
    if type(x) is str:
        strx = x
        x = getattr(traj, x)
        xl = '%s / %s' % (strx, getattr(x, 'units', 'dimensionless'))
    if type(y) is str:
        stry = y
        y = getattr(traj, y)
        yl = '%s / %s' % (stry, getattr(y, 'units', 'dimensionless'))
    plt = pylab.plot(x, y, **kwargs)
    pylab.xlabel(xl)
    pylab.ylabel(yl)
    pylab.grid()
    return plt
