+ /* @@@@
+ Things to deal with:
+ * After exchange_types the type has two entries in the list of
+ all types in irp. So far this is fine for the walker.
+ Maybe it's better to remove the id entry and shrink the list.
+ Does this conflict with the walker? Might a type be left out
+ during the walk?
+ * Deallocation: if the Id is removed from the list it will eventualle
+ disappear in a memory leak. When is impossible to determine so we
+ need to hold it in a seperate list for deallocation.
+ */