have ⟨thm₂⟩ := l₁
f P Q : Form
prf₁ : BProof BTheory P
thm₁ : BTheorem (P⊃Q)
ih : BTheory⊢P → P ∈ BTheory
h₁ : BTheory⊢Q
l₁ : P ∈ BTheory
⊢ Q ∈ BTheory
f P Q : Form
prf₁ : BProof BTheory P
thm₁ : BTheorem (P⊃Q)
ih : BTheory⊢P → P ∈ BTheory
h₁ : BTheory⊢Q
l₁ : P ∈ BTheory
thm₂ : BTheorem P
⊢ Q ∈ BTheory