{pu : Lean.Compiler.LCNF.Purity} →
  (motive : Lean.Compiler.LCNF.Arg pu → Sort u_1) →
    (arg : Lean.Compiler.LCNF.Arg pu) →
      ((fvarId : Lean.FVarId) → motive (Lean.Compiler.LCNF.Arg.fvar fvarId)) →
        ((x : Lean.Compiler.LCNF.Arg pu) → motive x) → motive arg