Debug
-----

1) EmptyMatch.xre
   My implementation doesn't distinguish between an empty 
   binding and a non-existent binding. This example shows it
   (z doesn't appear in the final list of bound variables as 
   it binds with an empty value).
   This is not really a bug or a problem at this moment, but take care
   of this. This example let me allowed to fix a bug (to output an empty 
   variable).

2) UnambigWrtInput.xre (WRT = With Respect To)
   This example shows an ambiguous pattern that is unambiguous with respect
   to the input type

3) Recursion.xre
   This examples shows both a correct way of self recursion and a correct 
   way of mutual recursion between type identifiers.
   It comes with two sample XML documents: SelfRecursion.xml and
   MutualRecursion.xml. 
   In the past running this example as a generic check let me to see
   a bug in the program.

4) ExactOutputType.xre
   This example shows a problem with variable bindings in alternatives, i.e.
   the fact that in some cases a type larger than the exact one is inferred for
   variables. Also if this seems a conservative choice it will give problems
   in some cases (see the example comment for details).
   XRel inherits this problem from XDuce (actually XDuce 0.4.0 has the same
   problem).

5) AmbiguityChk.xre
   A simple example that shows ambiguity in a pattern
   
6) Intersection.xre
   A simple intersection test
   
7) Difference.xre
   A simple difference test

To add
------

- exhaustivity.xre

An exhaustivity condition fail

- redundant.xre

An irredundancy condition fail

- chkoutputtype

A check against output type

Use cases
---------
- test "file not found" case

