Goal:
    A : Type  P : A → Type  Q : A → Type  Hl'1 : list A  Hl' : All Q Hl'1
  ============================
   ([] = Hl'1
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in All (λ x : A, P x × Q x) [])


DEBUG:Going to execute:
DepElim.introduce p
Level 2: evaluation returns
DepElim.introduce p; DepElim.elim_case p || destruct p || (case p; clear p)
where
p := Hl'
of type
constr of type tacvalue

Level 1: evaluation returns
DepElim.introduce p; DepElim.elim_case p || destruct p || (case p; clear p)
where
p := Hl'
of type
constr of type tacvalue