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