Multiple surface plots with correct z-ordering

Hi,

is it possible to create a three-dimensional plot with several surface
plots with correct z-ordering? The naive approach via

import pylab
from mpl_toolkits.mplot3d import Axes3D

pylab.close('all')
fig=pylab.figure()
ax=fig.add_subplot(111, projection='3d')

x=pylab.linspace(-8, 8, 128)
y=pylab.linspace(-8, 8, 128)
X, Y=pylab.meshgrid(x, y)
ax.plot_surface(X, Y, X**2+Y**2)
ax.plot_surface(X, Y, 100*pylab.ones_like(X), color='r')
pylab.draw()
pylab.show()

does not work. One surface plot is hiding the other one completely. I
am using Matplotlib version 1.1.1. May be one can combine the two
Poly3DCollections generated by plot_surface into a single one. Any
hints?

  Heiko

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