enrich
pathset,
posix-base
with
functions links : fid × directory-tree → pathset;
. + . : string × pathset → pathset;
axioms in-plinks : ⊦ p ∈ links(fid, tree) ↔ p ∈ tree ∧ tree[p] = fnode(fid);
in-consp : ⊦ p ∈ str + ps ↔ p ≠ ε ∧ p.head = str ∧ p.tail ∈ ps;
used for: ls;
end enrich