let todo_list = get_closure_coercions src tgt (uri,saturations,0) coercions in
debug_print (lazy("composed " ^ string_of_int (List.length todo_list)));
let todo_list = filter_duplicates todo_list coercions in
let todo_list = get_closure_coercions src tgt (uri,saturations,0) coercions in
debug_print (lazy("composed " ^ string_of_int (List.length todo_list)));
let todo_list = filter_duplicates todo_list coercions in