Goal:
    A : Type  n : nat  P : A → bool  d : A  H : is_true true  H0 : S n < 0
  ============================
   (∃ x : A, d = x ∧ P x)


DEBUG:Going to execute:
try (solve [ inversion H ])
DEBUG LTAC Evaluated term: H0
DEBUG LTAC Evaluated term: (S n < 0)
Level 2: type of H
 has value 
(S n < 0)