Changing subsection from numeric to alphabetical

How would I change subsections from being name 1.1, 1.2 to 1a, 1b? And are there any good templates for problem sets/college homework?

You can put the following in your preamble (Document -> Part -> Show preamble). Make sure to paste it in by doing Edit -> Paste from -> TeXmacs.


There is an interesting example by @fbob on tm-forge: