How can I create a smart collection that checks for only *one* given keyword in Lightroom 3?

Question

I think I know my Lightroom pretty well, but I couldn't find a way to create a smart collection that returns photos containing only *one* given keyword. Just one. Say, all photos containing *only* the 'foo' keyword, no other keywords.The only solution I found was: 1. create a smart collection that returns photos containing that given keyword 'foo', 2. select all photos and add them to *another collection* (say 'temp') for backup, 3. remove the given keyword 'foo' from the photos, 4. create a smart collection that returns the photos containing *no keywords*: this should return all the photos that *only* had the 'foo' keyword before I removed it in the previous step. Unfortunately all photos that had no keywords *before* step 3 will be returned as well, but that's OK, I don't have such photos. 5. do something with the photos returned by step 4, then go to the 'temp' collection and add the 'foo' keyword back.Tedious.

Answer 1

Try this:

Keywords: "contains words" (not "contains" or "contains all"): " foo "

Type word with space before and after; otherwise, the collection might include "food." Don't include quotation marks though.

That works for me with latest version of LR Classic; LR 3 is pretty old, hopefully it will work on that version too.