+ Definition fToCx {Γ}{Δ}{a1}{a2}{a3}{l} Σ :
+ ND Rule [] [ Γ > Δ > [] |- [(a1 ---> a2) ---> a3 ]@l ] ->
+ ND Rule [Γ > Δ > Σ,,[a1 @@ l] |- [a2]@l ]
+ [Γ > Δ > Σ |- [a3]@l ].
+ intro pf.
+ eapply nd_comp; [ eapply nd_rule; eapply RLam | idtac ].
+ set (fToC1 pf) as pf'.
+ apply boost.
+ apply pf'.
+ Defined.
+