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

  let max = ./max.dhall nix

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

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

  in  listMax