 We will return to SOD briefly in  section 3.2  below. Note here however that Hintikka (1970, 1973) mounted a technically heroic if ultimately unsuccessful attempt to solve it (see Sequoiah-Grayson (2008)), and for a properly detailed investigation, see the entry on  logic and information.  For now we must recognise that the response of Bar-Hillel and Carnap above brings with it some noteworthy philosophical claims of its own. Firstly, Bar-Hillel and Carnap are suggesting that the type of information which is encoded by logical truths and for which the amount encoded is non-zero, is psychological in some sense or other. Furthermore, it may vary for one person from the other even with respect to the same logical truth. Secondly, they are heeding the following advice of Claude Shannon, the originator of the mathematical theory of communication, given just two years earlier.