This meta post from a couple of months ago asks what to do when one tag is a subset of another. The specific example there was hat-puzzle as a subset of logic-puzzle. The result was that hat-puzzle was made a synonym of logic-puzzle, and the meta question was tagged status-completed.
It is still not clear to me if there is a general policy for dealing with situations like this. Specifically, I am wondering about math. There are several tags (perhaps combinatorics, calculation-puzzle,probability,...) that seem to be a subset of math. I don't necessarily think it is a good idea to make the other tags synonyms of math, because the other tags carry more specific information. On the other hand, when someone searches for math puzzles, it might be nice if the other tags popped up as well.
Is it possible to have one tag marked as a subset of a second, so that a search for the second also finds posts tagged with the first?