SearchHistory

Records the history of currently open implicit searches.

A search history maintains a list of open implicit searches (openSearchPairs) a shortcut flag indicating whether any of these are by name (byname) and a reference to the root search history (root) which in turn maintains a possibly empty dictionary of recursive implicit terms constructed during this search.

A search history provides operations to create a nested search history, check for divergence, enter by name references and definitions in the implicit dictionary, lookup recursive references and emit a complete implicit dictionary when the outermost search is complete.