Imperative.MakeNumberedNodeSourceSame as MakeNode, but also remembers all built node in a hash-table so we can check if elements already have an associated node
module Elt : HetHashtbl.HETEROGENEOUS_HASHED_TYPEmodule Relation : Parameters.GENERIC_GROUPinclude sig ... endtype !'a parent = 'a MakeNode(Elt)(Relation).parent = | Node : 'b t * ('a0, 'b) Relation.t -> 'a0 parent| RootChecks if a node has already been constructed for the given element