Proof 01. 1 ⊢ A ∧ (B ∧ C), hypo. 02. 1 ⊢ B ∧ C, conj_elimr 1. 03. 1 ⊢ C, conj_elimr 2. conj_elimrr. ⊢ A ∧ (B ∧ C) → C, subj_intro 3.