That is indeed what I wanted to do. And I understand it, now I see that it is wrong, while before reading you I though it was right. Some weird chemicals at my brain...
The problem is that the tiddler has "other tiddlers pointing" to it, and that does not involves any field on the tiddler itself. I want to remove those tiddlers that are not referenced from other tiddlers, but I think that is not actually possible in a single filter.
Many thanks