Fix multi-cite
Spelling
Clarify when I'm talking about what language
"Equational reasoning" --> "Applying equations"

Equational reasoning kind of means

        Reasoning using the fact that 'lhs <===> rhs'

But I wanted to focus more on an evaluation strategy, a way that is
similar to how Haskell is actually doing evaluation. By using the term
applying equations, I hope to convey:

        An algorithm doing 'lhs ====> rhs'

Note the one-way arrow. Since I did use the term equational reasoning at many
places, I took the opportunity to rephrase all paragraphs
using that terminology. In general I tried to take 2.2.2 towards more of
a introductory textbook-chapter. I try to say "You can evaluate your own
Haskell expressions by hand this way" rather than "This is how GHC
implements it".