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

  let Set/mergeAttrs = ../Set/mergeAttrs.dhall nix

  let extends
      : (Set → Set → Set) → (Set → Set) → Set → Set
      = λ(f : Set → Set → Set) →
        λ(rattrs : Set → Set) →
        λ(self : Set) →
          let super = rattrs self in Set/mergeAttrs super (f super self)

  in  extends