∀ {α : Type u_1} [inst : LE α] [inst_1 : DecidableLE α] [inst_2 : Std.PRange.UpwardEnumerable α]
  [inst_3 : Std.Rxc.IsAlwaysFinite α] [inst_4 : Std.PRange.LawfulUpwardEnumerable α] {xs : Std.Rcc α},
  xs.toList ++ [] = xs.toList