src/Pure/Concurrent/task_queue.ML

 fun group_tasks (Queue {groups, ...}) gs =
   fold (fn g => fn tasks => Tasks.merge (tasks, get_tasks groups (group_id g)))
     gs Tasks.empty
   |> Tasks.dest;
 
-fun known_task (Queue {jobs, ...}) task = can (Task_Graph.get_entry jobs) task;
+fun known_task (Queue {jobs, ...}) task = Task_Graph.defined jobs task;
 
 
 (* job status *)
 
 fun ready_job (task, (Job list, (deps, _))) =