First see ../../README.

In this directory, Regular.hs illustrates a test involving IO -- writing
and reading expressions to/from a file.  The use of 'smart constructors'
in the series definition is necessary for the property to hold, but does
*not* reduce the number of tests -- rather, there are duplicated tests for
the same expressions generated in different ways. Compile or interpret
Regular.main for a self-introducing test.