∀ (i : ℕ) (code : Lean.Compiler.LCNF.Code),
  i > 0 →
    ∀ (decl : Lean.Compiler.LCNF.FunDecl),
      InvImage (fun x1 x2 => x1 < x2) (fun x => PSigma.casesOn x fun i code => i)
        ⟨i - 1, Lean.Compiler.LCNF.Code.fun decl code⟩ ⟨i, code⟩