Page 124

Location: Chapter 12, Exercise 5(a) at end of chapter

It is (requirement on the bird)

$\Gamma xyzwv = y(zw)(xywv)$

$\Gamma xyzwv = y(zw)(xyzwv)$

The need for the missing variable in the definition can be confirmed by plugging in the solution for $\Gamma$ given a few pages later.