-Exchange: Γ, x:A, y:B, Δ |- R:C
- -------------------------------
+ Γ, x:A, y:B, Δ |- R:C
+Exchange: -------------------------------
Γ, y:B, x:A, Δ |- R:C
Γ, y:B, x:A, Δ |- R:C
-Contraction: Γ, x:A, x:A |- R:B
- --------------------------
+ Γ, x:A, x:A |- R:B
+Contraction: --------------------------