Goal:
    A : Type  B : Type  P : A → B → Prop  t : B  e : None = Some t
  ============================
   (∃ t' : A, nth_error [] 0 = Some t' ∧ P t' t)


DEBUG:Going to execute:
<coq-core.plugins.ltac::discriminate@0>
DEBUG LTAC Evaluated term: n
DEBUG LTAC Evaluated term: h