What each node reaches, joined over everything it leads to: of(n) = own(n) joined with of(s) for every successor s.
of(n) = own(n)
of(s)
s
the nodes a node leads to, asked for once per node
what a node contributes itself, asked for once per node after its successors
joins the values, its concat may return either of them if it subsumes the other but must not change them
concat
What each node reaches, joined over everything it leads to:
of(n) = own(n)joined withof(s)for every successors.