[sunshowers]

(Commit mutability separation, like many of jj's other features, was originally implemented in Mercurial.)

[saghm]

Good to know! I guess the "innovative" part was being able to apply these semantics on top of git without breaking compatibility.

[sunshowers]

Yeah. In Mercurial the set of immutable heads is state that's stored in the repository. In Jujutsu this is done via a revset, which is a really clever approach.