rcases e with ⟨rfl⟩
L : Language
Δ✝ Δ₁ Δ₂ Γ✝ : Sequent L
p q r : SyntacticFormula L
C : Set (SyntacticFormula L)
Δ Γ : Sequent L
e : Δ = Γ
d :  ⊢¹ Δ
⊢ CutRestricted C (Derivation.cast d e) ↔ CutRestricted C d
case refl
L : Language
Δ✝ Δ₁ Δ₂ Γ : Sequent L
p q r : SyntacticFormula L
C : Set (SyntacticFormula L)
Δ : Sequent L
d :  ⊢¹ Δ
⊢ CutRestricted C (Derivation.cast d ⋯) ↔ CutRestricted C d