A Study of Nāgārjuna's Twenty Verses on the Great Vehicle (Mahāyānaviṃśikā) and His Verses on the Heart of Dependent Origination (Pratītyasamutpādahṛdayakārikā) with the Interpretation of the Heart of Dependent Origination (Pratītyasamutpādahṛdayavyākhyāna).