Add Sec. 2.3
Bugfix

exSize3 appears in next commit.
Add Sec. 3.1
Simplify matching in paper

I realized this could be simplified by comparing with other code.
However, one must reorder the clauses to avoid changing the meaning of
the default case.
Sec. 3.2
Showcase pattern synonyms + view patterns

Compare optAddTop and optAddRule: the latter looks comparable to a
standard pattern matching, and the encoding overhead is reduced to the
occurrences of :$ and to using yet another identifier referring to the
`ADD` and `NUM` constructors. Bidirectional patterns could simplify even
that, I guess.