Oh well, I found the issue.

It was because of my special system. The printed representation of unify
variables
that point to a point to a point to a symbol got printed as a symbol. I
really need to tweak
the output to hint if it is a unify variable. And if wingo managed to
squeeze in tagging - so
much sweeter.

Anyway I have implemented

Subtypes
Parameter types
Recursive types
============

Now, the subtypes have been tested a little, the rest remains to be
debugged.
Also there is a weak key map of functions to types of the object that I use
to
record type signatures.

/Stefan