Goal:
    A : Type  t : A  P : A → A → Type  hd' : A  tl : list A  p : P t hd'
  ============================
   (t = hd')


DEBUG:Going to execute:
constructor 1
Level 4: evaluation returns
<coq-core.plugins.tauto::is_unit_or_eq@0>
where
tauto_flags := 
of type
tauto_flags
X1 := t = hd'
of type
constr of type tacvalue