Before:

 (let ((k158 (##core#lambda (r159)
   (let ((a157 r159)) (ok?3 k150 row12 a153 a157)))))
   (cdr k158 placed14))

After (???):

(let ((k158 (##core#lambda (r159)
  (ok?3 k131 row12 r155 r159))))
  (cdr k158 placed14))

Not sure if this is the same optimization, but an anonymous lambda was removed.