U60.show.go
: ∀(n: #U60) String.Concatenator
= λn
  #match x = #(< n #10) {
    #0: λnil
    (U60.show.go
      #(/ n #10)
      (String.cons #(+ #48 #(% n #10)) nil)
    )
    #+: λnil (String.cons #(+ #48 n) nil) 
  }: String.Concatenator