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

  let Number/subtract = ../Number/subtract.dhall nix

  let Number/toDouble = ../Number/toDouble.dhall nix

  in  λ(a : Double) →
      λ(b : Double) →
        Number/toDouble
          (Number/subtract (Number/fromDouble a) (Number/fromDouble b))