Conditional suppression formula PLEASE HELP

I have Crystal reports 8.5 and Im trying to generate a report that will give all of my sales orders with the part numbers price and the address they shipped to but I keep getting alot of duplicate fields so I used a suppresion forumla below

{InvoiceDetail.PartNumber} = previous({InvoiceDetail.PartNumber})

That did a great job of eliminated the duplicates but I found out that I have some orders that are in succesion with identical part numbers and they were being suppressed so I tried this formula

{InvoiceDetail.PartNumber} and {InvoiceHeader.SONumber} = previous({InvoiceDetail.PartNumber}) and {InvoiceHeader.SONumber}

thinking that will suppress any field that has the same part number and so number but it errors our and tells me I need a boolean.

I've tried just about everything and Im sure im missing something very simple but I dont know what it is.

PLEASE HELP{InvoiceDetail.PartNumber} and {InvoiceHeader.SONumber} = previous({InvoiceDetail.PartNumber}) and {InvoiceHeader.SONumber}

The very first thing is try to find out why you are getting duplicate data. Something must be wrong with you linking.

To suppress try this:

{InvoiceDetail.PartNumber} = previous({InvoiceDetail.PartNumber}) AND {InvoiceHeader.SONumber} = previous({InvoiceHeader.SONumber})