[Zope-CMF] I do not understand topic

[robert at rocad]

Hi there,
I am tyiing to use topics

to this aim I am creating documents having keywords in subject
like
'Doc a' : keywords a, b
'Doc b' : keywords a, c

now I create a topic 'show A' with two subtopics 'show B' and 'show C'

each of them have a string criterion, Criteria Type : Subject, values a,b,c
respectively.

What I expect to see is: under Topic 'show A'  the documents 'Doc a' and
'Doc b'
and 'Doc b' or 'Doc c' under the subtopics.

However I see nothing in all of them.

Where is my thinking gone astray ?

thanks for your help

Robert