Goal:
  
  A : Type
  B : Type
  P : list A → list A → A → A → B → Type
  ls2 : list A
  ls3 : list A
  H : [] ≠ []
  ============================
   (#|ls3| = #|ls2|)


DEBUG:Going to execute:
<coq-core.plugins.ltac::trivial@0> $1 $2