External aids to interpretation:- Dictionary : Ramavtar vs state tax officer (beetle leaves) : Motipur Jamindari vs State of Bihar (sugarcane) Books : Keshvanand Bharati vs Union of Inida Historical Background : Hariprasad vs Divakar Legislative History : A.k gopalan vs state (disallowed speech) : Keshvanand Bharati vs state of kerala (disallowed speech in parliament) : Indra swahney vs uoi (permitted speech of br Ambedkar for definition of backward classes)