Goal:
  
  A : Type
  B : Type
  R : A → B → Type
  R' : ∀ (a : A) (b : B), R a b → Type
  H : True
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in All2_dep_nil = All2_dep_nil)


DEBUG:Going to execute:
DepElim.introduce p
Level 6: evaluation returns
DepElim.introduce p; DepElim.elim_case p || destruct p || (case p; clear p)
where
p := H
of type
constr of type tacvalue

Level 5: evaluation returns
DepElim.introduce p; DepElim.elim_case p || destruct p || (case p; clear p)
where
p := H
of type
constr of type tacvalue