[Zope] Intersection/Union of ZCatalog result sets

I have found some old references to proposals for implementing the ability to combine (intersection, union) the result sets from multiple ZCatalog queries. Does anyone know if the ability to combine two or more 'lazy result sets' has been implemented? Hunting through the zope source code the only similar routines I could find were in the BTrees and ZCTextIndex code, but they deal with intersection/union of BTrees (not lazy result sequences). As an alternative, is there any way to get ZCatalog search results in 'BTree' form instead of lazy results? Thanks, Jonathan