Ladewig Petersen, E. M. M. Postan: Essays on Medieval Agriculture and General Problems of the Medieval Economy. Cambridge, at the University Press, 1973. - Viii + 302 s.; £4.80. M. M. Postan: Medieval Trade and Finance. Cambridge, at the University Press, 1973. - Vii + 382 s.; £5.00. ht 1974, 13.