let filter_solutions (group : string hashset)
(graphlist : graph list) : graph list =
let not_empty graph =
let has_empty_lang n =
let pred_node = find_node graph n in
match pred_node.lang with
| Machine x -> if Nfa.is_empty x then
(true) else false
| _ -> false
in
not (exists has_empty_lang group)
in
List.filter not_empty graphlist