“…Various practical applications for such models have been found in recent years; see, for example, Sprent (1961), Hudson (1966), Dunicz (1969), Owen, Davis and Ridgman (1969), Williams (1970), Bacon and Watts (1971) and Kirby (1974). Various practical applications for such models have been found in recent years; see, for example, Sprent (1961), Hudson (1966), Dunicz (1969), Owen, Davis and Ridgman (1969), Williams (1970), Bacon and Watts (1971) and Kirby (1974).…”