While I do agree with you about Haskell's close association with maths (and an assumption about the users), in this case the author is pursuing a mathematical p

While I do agree with you about Haskell's close association with maths (and an assumption about the users), in this case the author is pursuing a mathematical proof (or rather, a counterexample to a mathematical hypothesis). The use of Haskell here is just as a tool to that end. It is therefore reasonable to expect a greater than normal amount of mathematical notation.