Pārisuddhi-padhāniyanga: the 4 'elements of the effort for purity', are: effort for purity of morality sīla-parisuddhi-padhāniyanga for purity of mind citta of view ditthi of deliverance vimutti Cf. A. IV, 194. - Another 9 factors are enumerated in D. 34, namely the 7 'stages of purification see: visuddhi and the effort for purity of higher knowledge vijjā-p. p and of deliverance vimutti.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.