Goal:
    A : Type  l : list A  n : nat  H : n < #|l|  Heq_l : [] = l
  ============================
   A


DEBUG:Going to execute:
subst *
Level 0: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.
Level 0: Backtrace:

Failed to progress.