Location: Chapter 21, solution to Problem 2, second paragraph
It is (solution, second method)
Using the second method, you should get the solution W'W', where W' is the converse warbler -- W'xy = yxx. If you get CW(CW) you are also right, since CW is a converse warbler. You can easily check that W'W'x=x(W'W').
It should become
Using the second method, you should get the solution CL(CL), equivalent to the longer S,K,I-expression A_2A_2 where A_2=S(K(SI))(S(KK)(SII)).
The second method requires first to find a bird satisfying A_2yx=x(yy); either by the algorithm illustrated in Chapter 18 or by direct derivation, one finds the above result
leading to the right solution.
The expression given in the text does not fulfill the requirement: indeed,
where the parentheses are required if one is to honour the original expression given in the Problem of finding a bird A such that Ax=xA for any x.