@
transistor - have a look at User Categories, see ==>>
Tag browser
They provide the means to associate a set of individual category items (Authors, Publishers, Tags etc) into arbitrary groups. So, tags
module theory and
linear algebra would be members of the
algebra user category, when you tagged a book with
module theory it would appear in the
algebra user category automatically.
You define them via this:
And there is a User Category optional plugin, it makes maintenance of them easier.
BR