Clarification in ch 5 vol 1

Hi!

Thanks for great tutorial! I just started to learn Haskell, while deepening knowledge about functions in chapter 5, found it confusing that term has apostrophe as part of its name. It will be great if you could add example call after defining this, or add info that apostrophe is valid symbol in variables. Later I noticed syntax coloring and it became clear. Its surprising if one came from language which doesn't allow this.