I have three classes Master() private Set<Header> Headers; ---------------------------- Header() private Set<Line> Lines; ---------------------------- Line() private String name; ---------------------------- Master() is the facts. In my spreadsheet I would like to check the line name == "abc". How do I do that. Here is what I got but it cause type mismatched error!! please help. Master() $h: Headers $L : $h.Lines m: Line(<generated by condition header>) from $L Please help!! -- View this message in context: http://drools.46999.n3.nabble.com/How-to-deal-with-Set-inside-another-Set... Sent from the Drools: User forum mailing list archive at Nabble.com.