I omitted this from the readings above. If you're interested, look at the following sections of the OU book:
There's a nice half-page explanation of minimaxing in Chess playing programs and the problem of complexity by A Newell, J C Shaw and H A Simon, in Computers and Thought edited by E A Feigenbaum and J Feldman: RSL; Psychology: KH:F.
For a discussion of the limitations of minimaxing, look at the article by Berliner in Thinking --- Readings in Cognitive Science, edited by P.N.Johnson-Laird and P.C.Wason (CUP, 1977).