Whoa, actually that seems to work!  But now I have other functions that also throw “undefined” errors, such as torch.flip() not being supported.
And my new DIY implementation of torch.flip() relies on torch.arange() which throws an ONNX export error about “index” not existing.
…bah.  This is no fun.  Is ONNX still the only way to get to Tensorflow from PyTorch?
(This is for a web app.  We may just go with Bokeh Server.)