(recListFOps: RecListFOps[RecListFOps[T, A], A]).find(cond)
(recListFOps: RecListFOps[RecListFOps[T, A], A]).headOption
(recListFOps: RecListFOps[RecListFOps[T, A], A]).length
(recListFOps: RecListFOps[RecListFOps[T, A], A]).tailOption
(recListFOps: RecListFOps[RecListFOps[T, A], A]).take(i)(N, C)