eco subset
part of
in branching relationship with
main stem of
In the tree T depicted in https://oborel.github.io/obo-relations/branching_part_of.png, S is the main stem of T. There are no other main stems. If we were to slice off S to get a new tree T', rooted at the root of B1, then B1 would be the main stem of T'.
x main_stem_of y if y is a branching structure and x is a channel that traces a linear path through y, such that x has higher capacity than any other such path.
Chris Mungall
requires discussion