Rules and rulesets in Workflow 4
It's always difficult to find the lack of something in a search engine. Rulesets, a feature of Workflow 3, are not a feature of version 4, so it might be frustrating to try to deduce this from the existing documentation.
When conditional operations are needed in WF4, the If activity is the option of choice- there is no corresponding Policy activity in WF 4 to encapsulate conditions. Rules in WF4 can thereby be implemented as a series of If activities. Forward-chaining is not a feature that this can implement.
If existing conditions from WF 3 need to be used in WF 4, or if forward chaining is needed, the WF3 Policy activity can be used for this; see the Using Variables with a .NET Framework 3.5 Ruleset sample (https://msdn.microsoft.com/en-us/library/dd807380.aspx) for details on how to implement.
For further information on using rules in WF4, see the migration guideline documents here: https://www.microsoft.com/downloads/en/details.aspx?FamilyID=bd94c260-b5e0-4d12-93ec-53567505e685&displaylang=en