DOCBOOK: ISO Entities

["Kaiser Christian (SV SC RS T33)" <Christian.1.Kaiser@at.siemens.de>]

>/ "Kaiser Christian (SV SC RS T33)" <Christian.1.Kaiser@at.siemens.de> was
heard to say:
>| how can implement symbols such as....
>| 
>|       "DOES NOT CONTAIN AS NORMAL SUBGROUP"  <!-- iso-amsn seems to be
>| responsible -->
>| 
>| I know the Identifier to use is .... 
>| 
>|       PUBLIC "ISO 8879:1986//ENTITIES Added Math Symbols: Negated
>| Relations//EN//XML"
>| 
>| What do I have to do with it?
>
>That depends on what your processing system is. Are you using SGML or
>XML? What tool are you rendering with? What do you want the implementation
>to do?
>
>                                        Be seeing you,
>                                          norm

I'm using XML DocBook 5.0 with Xalan (+ FOP) to create HTML (and PDF)
output.
I'm sorry, I think chose the wrong word by using "implementation".
All I want to see as a result is a mathematical symbol within my output.

I've seen in your (really good) "DocBook Definition Guide" at ...

    http://docbook.org/tdg/en/html/appb.html#xml-sdata

... a example: it puts the trade sign into document.
    Some kind of:
    ... <!ENTITY trade "&#x2122;"> ] <book> ... &trade; ...
... has to be within the DOCTYPE def. 

This example works fine, 
... but it does not with 

    <!ENTITY nsube "&#x2288;">

The nsube Symbol is defined at
    http://docbook.org/tdg/en/html/iso-amsn.html

So, what do I have to do to make my "Neither a subset of nor equal to" -sign

visible in the output?
I guess I have to use the ...
"ISO 8879:1986//ENTITIES Added Math Symbols: Negated Relations//EN//XML"
Identifier. But how?

Thank you very much for your help.
Chris