Library prosa.implementation.facts.job_constructor

In this file, we prove facts about the job-constructor function when used in pair with the concrete arrival sequence.
Section JobConstructor.

Assume that an arrival curve based on a concrete prefix is given.
  #[local] Existing Instance ConcreteMaxArrivals.

Consider a task set ts with non-duplicate tasks.
  Variable ts : seq Task.
  Hypothesis H_ts_uniq : uniq ts.

First, we show that generate_jobs_at tsk n t generates n jobs ...
  Lemma job_generation_valid_number:
     tsk n t,
      tsk \in ts size (generate_jobs_at tsk n t) = n.
    movetsk n t IN.
    by rewrite size_map size_iota.

... and that each generated job is unique.
  Lemma generate_jobs_at_unique:
     tsk n t,
      uniq (generate_jobs_at tsk n t).
    movetsk n t.
    rewrite /generate_jobs_at //= /generate_job_at map_inj_uniq //=;
      first by apply iota_uniq.
    by movex1 x2 /eqP /andP [/andP [/andP [/andP [//= /eqP EQ _] _] _] _].

Next, for convenience, we define arr_seq as the concrete arrival sequence used with the job constructor.
We start by proving that the arrival time of a job is consistent with its positioning inside the arrival sequence.
  Lemma job_arrival_consistent:
     j t,
      j \in arrivals_at arr_seq t job_arrival j = t.
  Proof. by movej t /mem_bigcat_exists [tsk [TSK_IN /mapP [i INi] ->]]. Qed.

Next, we show that the list of arrivals at any time t is unique ...
  Lemma arrivals_at_unique:
      uniq (arrivals_at arr_seq t).
    apply bigcat_uniq ⇒ //=;
      first by movetau; apply: generate_jobs_at_unique.
    movej task1 task2 /mapP[i1 IN1 EQj1] /mapP[i2 IN2 EQj2].
    by move: EQj1 EQj2 ⇒ → [_].

... and generalize the above result to arbitrary time intervals.
  Lemma arrivals_between_unique:
     t1 t2,
      uniq (arrivals_between arr_seq t1 t2).
    movet1 t2.
    rewrite /arrivals_between.
    apply bigcat_nat_uniq.
    - by apply arrivals_at_unique.
    - movej jt1 jt2 IN1 IN2.
      by move: (job_arrival_consistent j jt1 IN1)
                 (job_arrival_consistent j jt2 IN2) ⇒ <- <-.

Finally, we observe that generate_jobs_at tsk n t indeed generates jobs of task tsk that arrive at t
  Corollary job_generation_valid_jobs:
     tsk n t j,
      j \in generate_jobs_at tsk n t
            job_task j = tsk
             job_arrival j = t
             job_cost j task_cost tsk.
  Proof. by movetsk n t j /mapP [i INi] →. Qed.

End JobConstructor.