Goal:
  
  A : Type
  P : A → Type
  p : A → bool
  q : A → bool
  x : A
  l : list A
  p0 : P x
  X : All P l
  IHX : (∀ x : A, P x → p x = q x) → forallb p l = forallb q l
  H : ∀ x : A, P x → p x = q x
  ============================
   (p x && forallb p l = q x && forallb q l)


DEBUG:Going to execute:
assert X2
Level 1: evaluation returns
assert X2; [ exact (id0 id1) | clear id0 ]
where
id1 := x
of type
intropattern
id0 := p
of type
intropattern
flags := 
of type
tauto_flags
X2 := bool
of type
constr of type tacvalue