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:

Txy=S(K(SI))Kxy=K(SI)x(Kx)y= SI(Kx)y=Iy(Kxy)=yx\;.