Goal:
  
  A : Type
  v : A
  _a_ : A
  _l_ : list A
  _n_ : nat
  p : hd_error (skipn _n_ _l_) = Some v
  ============================
   (locked false = true)


DEBUG:Going to execute:
Ltac.assumption
DEBUG LTAC Evaluated term: not_locked_false_eq_true