| RJoin : ∀ Γ Δ Σ₁ Σ₂ τ₁ τ₂ l, Rule ([Γ > Δ > Σ₁ |- τ₁ @l],,[Γ > Δ > Σ₂ |- τ₂ @l]) [Γ>Δ> Σ₁,,Σ₂ |- τ₁,,τ₂ @l ]
-(* order is important here; we want to be able to skolemize without introducing new RExch'es *)
+(* order is important here; we want to be able to skolemize without introducing new AExch'es *)
| RApp : ∀ Γ Δ Σ₁ Σ₂ tx te l, Rule ([Γ>Δ> Σ₁ |- [tx--->te]@l],,[Γ>Δ> Σ₂ |- [tx]@l]) [Γ>Δ> Σ₁,,Σ₂ |- [te]@l]
| RLet : ∀ Γ Δ Σ₁ Σ₂ σ₁ σ₂ l, Rule ([Γ>Δ> Σ₁ |- [σ₁]@l],,[Γ>Δ> [σ₁@@l],,Σ₂ |- [σ₂]@l ]) [Γ>Δ> Σ₁,,Σ₂ |- [σ₂ ]@l]