Goal:
    A : Type  f : nat → A  n : nat  Hn : nth_error [] n = Some (f n)
  ============================
   (n < 0)


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrrewrite@0> $1 $2
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 1: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 2: Backtrace:

Tactic failure:  Cannot find witness.
Level 3: Backtrace:

Tactic failure:  Cannot find witness.
Level 2: Backtrace:

Tactic failure:  Cannot find witness.
Level 1: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 1: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 1: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 1: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.
Level 1: Backtrace:

Tactic failure:  Cannot find witness.
Level 0: Backtrace:

Tactic failure:  Cannot find witness.