Gets a Python
dict of the unbound references in
) -> Dict[
Compuations that are equal will have the same collections of unbounded
references, so it is safe to use
comp as the key for this
dict even though
a given compuation may appear in many positions in the AST.
The computation building block to parse.
dict of elements where keys are the compuations in
values are a Python
set of the names of the unbound references in the
subtree of that compuation.