In git you can do something like HEAD~ to refer to the parent commit of HEAD. Mercurial has a similar feature called revsets which JJ took inspiration from (including the name). The revset language is a declarative query language—not unlike SQL—that lets you specify a set of revisions (a revset) that match certain criteria. It ends up looking more like set operations than SQL, but the idea is similar. In JJ you can use @ to mean “the current commit”,...
