Goal:
  
  A : Type
  H : ReflectEq A
  l1 : list A
  l2 : list A
  call := split_prefix l1 l2 : (list A * list A * list A)%type
  ============================
   (let
    '(prefix, l1', l2') := call in l1 = prefix ++ l1' ∧ l2 = prefix ++ l2')


DEBUG:Going to execute:
subst call