Page 173

Location: Explanation of "The Secret", after Problem 4

It is (top of the page, lines 5-7)

... Therefore $S(K(SI))$ is a thrush. The reader can check this by computing $S(K(SI))xy$; he will end up with yx.

It should become

... Therefore $S(K(SI))K$ is a thrush. The reader can check this by computing $S(K(SI))Kxy$; he will end up with yx.

Short explanation

The final Kestrel in the expression for $T$ is needed, indeed: