It is necessary to search in the forum on a combination of parameters such as user, period, category themes (in the list or not list). Each topic should be able to install multiple categories, or you can use a set of prefixes. In the prefix will be the main topic category or prefix.
Often one topic relates to more than one category. Well, would like to have several categories of topics were added.
Now there is one in the topics "category" prefix.
Search by categories, time period, the user keyword and list of users.