Plus is used instead Add class

[yaitskov]

Section says that type should have an instance of class Plus to benefit from operator + though the correct class name for this operator is Add.

Please quote the text that is incorrect:

n the following type class declaration, Plus is the name of the class, α : Type is the only argument, and plus : α → α → α is the only method:

class Plus (α : Type) where
  plus : α → α → α

> MISTAKE GOES HERE