Goal:
  
  A : Type
  P : A → A → Type
  a : sigma
        (λ index : sigma (λ _ : list A, list A),
           OnOne2 P (pr1 index) (pr2 index))
  b : sigma
        (λ index : sigma (λ _ : list A, list A),
           OnOne2 P (pr1 index) (pr2 index))
  e : NoConfusion_OnOne2 A P a b
  ============================
   (noConfusion_OnOne2_obligation_2 A P a b
      (noConfusion_OnOne2_obligation_1 A P a b e) = e)


DEBUG:Going to execute:
PTRDEBUGTACCoreTactics.destruct_sigma a; CoreTactics.destruct_sigma b;
            destruct a; DepElim.depelim b; simpl in * |-;
            CoreTactics.on_last_hyp
             ltac:(fun id =>
                     hnf in id;
                      CoreTactics.destruct_tele_eq id || destruct id)
Level 3: evaluation returns
CoreTactics.destruct_sigma a; CoreTactics.destruct_sigma b; destruct a;
 DepElim.depelim b; simpl in * |-;
 CoreTactics.on_last_hyp
  ltac:(fun id => hnf in id; CoreTactics.destruct_tele_eq id || destruct id);
 (solve [ constructor ])
where
b := b
of type
constr
a := a
of type
constr of type tacvalue