For my current series of books that I'm writing in org-mode which is
being exported to latex, I need to differentiate between recipes in the
current working file, and to recipes in an external file. This is in a
series of books all containing recipes. So what I'm looking for is the
ability to use a single underline for internal, and a double underline
for external. I can do a single underline easily in org-mode, but I'm
having problems with a double underline.

But is it the best method, using single and double underlines? Can
anyone suggest some other ways of doing it, please? Like, for instance,
can I have a reference to a particular section in another file?

Thanks
Sharon
-- 
A taste of linux = http://www.sharons.org.uk
TGmeds = http://www.tgmeds.org.uk
DrugFacts = https://www.drugfacts.org.uk  
Debian 9.3, fluxbox 1.3.5-2, emacs 25.3.2, org-mode 9.1.4-2