(* MachStep that doesn't change the schedule, Reduces the set of valid schedules... *)
Inductive has_unique_running tp:Prop :=
| HasUniqueRun i (cnti : ThreadPool.containsThread tp i) q:
ThreadPool.getThreadC cnti = Krun q ->
has_unique_running tp.

Lemma csafe_first_tid:
forall n U U' tr tp m,
csafe (U, tr, tp) m n ->
schedPeek U = schedPeek U' ->
csafe (U', tr, tp) m n.