Goal:
  
  A : Type
  R1 : A → A → Type
  R2 : A → Type
  R3 : A → Type
  hd : A
  tl : list A
  tl' : list A
  o : OnOne2 R1 tl tl'
  IHo : All R2 tl
        → (∀ x : A, R2 x → R3 x)
          → (∀ x y : A, R1 x y → R2 x → R3 y) → All R3 tl'
  H1 : list A
  H : All R2 H1
  ============================
   (hd :: tl = H1
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in
      (∀ x : A, R2 x → R3 x)
      → (∀ x y : A, R1 x y → R2 x → R3 y) → All R3 (hd :: tl'))


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 := hd :: tl
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