Proof 01. 1 ⊢ A ∧ B ∧ C ∧ D, hypo. 02. 1 ⊢ A ∧ B ∧ C, conj_eliml 1. 03. 1 ⊢ A ∧ B, conj_eliml 2. 04. 1 ⊢ B, conj_elimr 3. conj_elimllr. ⊢ A ∧ B ∧ C ∧ D → B, subj_intro 4.