preemption_time.v should not depend on task concept

This is a purely accidental dependency; purge it.

restructuring/model/schedule/preemption_time.v

@@ -7,26 +7,16 @@ From mathcomp Require Import ssreflect ssrbool ssrfun eqtype ssrnat seq fintype
     ideal uni-processor model. *)
 Section PreemptionTime.
 
-  (** Consider any type of tasks ... *)
-  Context {Task : TaskType}.
-  Context `{TaskCost Task}.
-  Context `{TaskMaxNonpreemptiveSegment Task}.
-
-  (**  ... and any type of jobs associated with these tasks. *)
+  (**  Consider any type of jobs... *)
   Context {Job : JobType}.
-  Context `{JobTask Job Task}.
   Context `{JobArrival Job}.
   Context `{JobCost Job}.
 
-  (** In addition, we assume the existence of a function mapping a
-      task to its maximal non-preemptive segment ... *)
-  Context `{TaskMaxNonpreemptiveSegment Task}.
-
-  (** ... and the existence of a function mapping a job and
+  (** ... and assume the existence of a function mapping a job and
       its progress to a boolean value saying whether this job is
       preemptable at its current point of execution. *)
   Context `{JobPreemptable Job}.
-  
+
   (** Consider any arrival sequence with consistent arrivals. *)
   Variable arr_seq : arrival_sequence Job.
   Hypothesis H_arrival_times_are_consistent : consistent_arrival_times arr_seq.
@@ -35,7 +25,7 @@ Section PreemptionTime.
   Variable sched : schedule (ideal.processor_state Job).
   Hypothesis H_jobs_come_from_arrival_sequence:
     jobs_come_from_arrival_sequence sched arr_seq.
-  
+
   (** We say that a time instant t is a preemption time iff the job
       that is currently scheduled at t can be preempted (according to
       the predicate). *)
@@ -43,5 +33,5 @@ Section PreemptionTime.
     if sched t is Some j then
       job_preemptable j (service sched j t)
     else true.
-    
+
 End PreemptionTime.