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


DEBUG:Going to execute:
idtac
Level 3: Backtrace:

The type of A is not inductive.
Level 3: Backtrace:

No applicable tactic.