{pu : Lean.Compiler.LCNF.Purity} →
  {motive : Lean.Compiler.LCNF.Arg pu → Sort u} →
    (t : Lean.Compiler.LCNF.Arg pu) →
      t.ctorIdx = 2 →
        ((expr : Lean.Expr) → (h : pu = Lean.Compiler.LCNF.Purity.pure) → motive (Lean.Compiler.LCNF.Arg.type expr h)) →
          motive t