λ(nix : ../NixPrelude.dhall) →
  let max = ./max.dhall

  let Optional/map = ../Optional/map.dhall nix

  let listMax
      : List Natural → Optional Natural
      = λ(xs : List Natural) →
          Optional/map
            Natural
            Natural
            (λ(n : Natural) → List/fold Natural xs Natural max n)
            (List/head Natural xs)

  in  listMax