Goal:
  
  A : Type
  l3 : list A
  R1 : A → A → Type
  R2 : A → A → Type
  R3 : A → A → Type
  hd : A
  tl : list A
  tl' : list A
  o : OnOne2 R1 tl tl'
  IHo : ∀ l3 : list A,
          All2 R2 tl l3
          → (∀ x y : A, R2 x y → R3 x y)
            → (∀ x y z : A, R1 x y → R2 x z → R3 y z) → All2 R3 tl' l3
  H1 : sigma (λ _ : list A, list A)
  H : All2 R2 (pr1 H1) (pr2 H1)
  ============================
   ({| pr1 := hd :: tl; pr2 := l3 |} = H1
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in
      (∀ x y : A, R2 x y → R3 x y)
      → (∀ x y z : A, R1 x y → R2 x z → R3 y z) → All2 R3 (hd :: tl') l3)


DEBUG:Going to execute:
try rename id into id',id' into id
Level 3: evaluation returns
try rename id into id',id' into id; cont id'1 id
where
t := {| pr1 := hd :: tl; pr2 := l3 |}
of type
constr
id'1 := H1
of type
constr
id' := H
of type
ident
id := H
of type
ident
cont := fun id id' => DepElim.decompose_exists id id'
        where
        id := H
        of type
        ident
of type
tacvalue of type tacvalue