Sorry guys, I think I get it now. Since the conda install command refers to ‘pytorch’ and my Python code goes ‘import torch’ (rather than ‘import pytorch’), I assumed the import statement referred to (a Python wrapped) Lua torch. I guess the ‘py’ of ‘pytorch’ is skipped since we all know we’re writing Python :-).  This is what happens to you (i.e. me) when you copy sample code blindly.
I now think my problem may be with Conda. When I install a package, it giver this warning:
==> WARNING: A newer version of conda exists. <==
current version: 4.5.11
latest version: 4.8.3
Please update conda by running
$ conda update -n base -c defaults conda
But when I run the suggested command, it reproduces the warning, and claims all is installed:
==> WARNING: A newer version of conda exists. <==
current version: 4.5.11
latest version: 4.8.3
Please update conda by running
$ conda update -n base -c defaults conda
# All requested packages already installed.
I guess I should reinstall (Ana)conda?