1. DA Bell (1968) Information Theory and its Engineering Application, 4th edn, Sir Isaac Pitman & Sons, London.
2. M Broadbent (1984) Information management and educational pluralism, Education for Information 2: 209–227.
3. AG Cairns-Smith and H Hartman (1986) Clay Minerals and the Origin of Life, Cambridge University Press.
4. C Cherry (1978) On Human Communication, 3rd edn, The MIT Press, Cambridge, Mass.
5. AL Mackay (1986) The crystal abacus, in Clay Minerals and the Origin of Life (AG Cairns-Smith and H Hartman ed), pp. 140–143, Cambridge University Press.