+
+
+When pulling, which remotes get to update which branches ?
+Complicated question!
+
+For now, have "blessed" remotes, which we always pull and update from.
+All these count as sources above.
+
+Update operation restrictions available, which restrict use of various
+sources above ? What about implications for correctness of merge
+algorithm ?
+
+
+Concept of a "stack" ?
+Unnecessary - instead, deal with leaf branches
+Operations like "go up the stack", goes towards leaf. Hopefully unique.
+"Down" the stack, uses a "conventional" linearisation
+Stack reordering op ? auto adjust deps