Multiple aliases in Drupal
[To put this in something more resembling English, we're talking about creating multiple URLs, more than one web address, to one page or piece of content on a Drupal site.]
It's actually very easy. Go to admin/path/add and add another alias for the node which you want multiply aliased.
(Look up the node/## first by going to the node, and checking the node/##/edit path– you'll have to be logged in to see the edit link.)
So if it's that simple, why would this need an explanatory page on Agaric Design?
Well, if you try to add your alias by editing an existing path, it doesn't work. (For instance if you first tried to redirect from a new path alias to an existing alias, which really doesn't work, and then edited it to point to a system path, any existing alias to that system path gets replaced.)
And seeing the fact that changing foo/bar to foo path alias to foo/bar to node/7 made foo to node/7 disappear-- well, you might logically assume that Drupal isn't letting you have multiple aliases to node 7.
Not true. Adding an alias, instead of editing an existing one to point to the system path, will give you multiple path aliases to the same system path