Typo in gray box (line 12): “Indeed there is such _as_ class”

"You will see in Section 4 how to speed it up."

We're already in Section 16.6. The reference must be wrong?

Last paragraph, first sentence, first part:
"For associative operations, fold left and fold right are equivalent"
should be "For commutative associative operations, fold left and fold
right are equivalent".

Counter example for the statement as it stands:
scala> ( "START" /: words) ( _ + _ )
res10: String = STARTthequickbrownfox

scala> (words :\ "START" ) ( _ + _ )
res11: String = thequickbrownfoxSTART

Intro: While discussing type inference for fold methods, the books gives
a forward reference, which leads to the wrong chapter.

Text: "To find out why the type inferencer goes wrong, you’ll need to
know about the types of the fold methods and how they are implemented.
More on this in Chapter 22."

Problem: However, folds are not even discussed in chapter 22, and the
issue is discussed much earlier, in section 16.10.

Fix: Please replace last sentence of the quoted text with: "More on this
in Section 16.10."