Goal:
    A : Type  H : ReflectEq A  l1 : list A  l2 : list A  l : list A
  ============================
   (is_prefix l l1
    → is_prefix l l2 → is_prefix l (fst (fst (split_prefix l1 l2))))


DEBUG:Going to execute:
constr:(fun_elim)
Level 6: Backtrace:


Could not find an instance for "FunctionalElimination 
                                  (split_prefix l1) 
                                  ?fun_elim_ty ?n"
in environment:
A : Type
H : ReflectEq A
l1, l2, l : list A