1; \tau_2)} \; (16.2b)
  \quad \frac{\Delta \, \Gamma \vdash e_1 \, : \, \texttt{arr}(\tau_2 ; \tau) \quad \Delta \, \Gamma \vdash e_2 \, : \, \tau_2}{\Delta \, \Gamma \vdash \texttt{ap}(e_1 ; e_2) \, : \, \tau} \; (16.2c) \\
   \, \\
  \quad \frac{\Delta, t \, \textsf{type} \, \Gamma \vdash e \, : \, \tau}{\Delta \, \Gamma \vdash \texttt{Lam}(t.e) \, : \, \texttt{all}(t.\tau)} \; (16.2d)
  \quad \frac{\Delta \, \Gamma \vdash e \, : \, \texttt{all}(t.\tau&#39;) \quad \Delta \vdash \tau \, \textsf{type}}{\De