I am trying to write this validation rule

OR(AND($RecordType.Name ="Opportuntiy", ISPICKVAL( StageName , "Closed Won") ,ISBLANK(Revenue_Start_Date__c )))

This works but I need the Revenue Start date to be >= to close date thats on the Opportunity. 

how can I fix this rule to make it work. 

Thank you

I am trying to write this validation rule

OR(AND($RecordType.Name ="Opportuntiy", ISPICKVAL( StageName , "Closed Won") ,ISBLANK(Revenue_Start_Date__c )))

This works but I need the Revenue Start date to be >= to close date thats on the Opportunity. 

how can I fix this rule to make it work. 

Thank you