Thanks for those, I hadn't seen them. The Ritzau paper indeed appears to be doing something very similar, where in 5.2 he describes "inner references" whose lifetime is bounded by the outer one, I call that "borrowing", where the outer definition (the owner) gets locked from mutation during the borrow.

What I do is a bit more involved though, as for every language construct I indicate if it wants to own or borrow its children (and wether it wants the parent to own or borrow), to remove maximum refcounts, also for cases which are not simply variables. Again, I will describe this in detail.

The second paper I don't see how it relates to what I am doing.