redefinition of SimpleType in nested schemas

Hello.

I have an xml schema, let's call it dictionary.xsd, describing general
structures and datatypes used in dictionaries. dictionary.xsd contains a
definition of a SimpleType called Subjects. The SimpleType is a restriction
of xs:string and it contains a long list of enumerations.

Another - more specialized - schema, called Danish-English.xsd is built upon
dictionary.xsd. This is done by using <xs:include>.

A third - even more specialized - schema, called
Danish-English-technical.xsd builds on it's turn upon Danish-English.xsd,
but this time I have chosen to use <xs:redefine>, because in these special
dictionaries, I need to modify the SimpleType "Subject" by extension.

I cannot figure out how to do this. I am not allowed to do so.

This has worked for me with only one level of inclusion. Could the fact that
I want to redefine a schema on a level that is more than one nesting leve
l"away" be the problem?

below I have tried to illustrate the nesting and the Type Definitions:

Danish-English-technical.xsd (redefines SimpleType "Subjects")
->
redefines
Danish-English.xsd
->
includes
dictionary.xsd (declares SimpleType "Subjects" as a restriction of
xs:string by enumeration)

I would be grateful for any input.

Regards,
Marie