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


DEBUG:Going to execute:
F x2 x1 x0
Level 2: evaluation returns
<coq-core.plugins.tauto::find_cut@0>
where
k := fun id0 id1 X2 => assert X2; [ exact (id0 id1) | clear id0 ]
     where
     flags := 
     of type
     tauto_flags
of type
tacvalue of type tacvalue