I have two separated folders, each includes LyX files with the needed attachments (pictures...etc.) , I found that I need to to use zref-xr package to make hyper cross references between those files (non of them included in the other), what i can't understand (or find an answer) is what I should write in \zexternaldocument{????} should It be the full path to the second folder? or something else? some people speaks about .aux files that I don't understand where to find.
Another small question in the context: What is better (or should) use, xr package with hyperref package, or the above mentioned zref-xr ?