let empty_ugraph = empty_bag, UriManager.UriSet.empty, false
let oblivion_ugraph = empty_bag, UriManager.UriSet.empty, true
+(* FG: default choice for a ugraph ??? *)
+let default_ugraph = oblivion_ugraph
let current_index_anon = ref (-1)
let current_index_named = ref (-1)