Goal:
  
  A : Type
  B : Type
  P : A → B → B → Type
  b : A
  bs : list A
  hd : B
  tl : list B
  tl' : list B
  X : OnOne2All P bs tl tl'
  IHX : OnOne2All
          (λ (i : A) (x y : B),
             (∑ ni : nat, nth_error bs ni = Some i) × P i x y) bs tl tl'
  ============================
   (OnOne2All
      (λ (i : A) (x y : B),
         (∑ ni : nat, nth_error (b :: bs) ni = Some i) × P i x y) 
      (b :: bs) (hd :: tl) (hd :: tl'))


DEBUG:Going to execute:
<coq-core.plugins.ltac::constructor@0>