Proof 01. 1 ⊢ A ∧ B ∧ C, hypo. 02. 1 ⊢ A ∧ B, conj_eliml 1. 03. 1 ⊢ A, conj_eliml 2. conj_elimll. ⊢ A ∧ B ∧ C → A, subj_intro 3.