PXProcessing BQL Question

Hello, 

I am creating a processing screen that pulls in shipment records of the receipt type and running into a small issue when creating the BQL statement to do so. You’ll notice below I am trying to join an enclosed condition with the condition to check if the shipment is of the type receipt. I’m not entirely sure what to add inbetween the commas after the “Where<SOShipment.Operation,” as I can’t simply type “R” (value stored in SQL). Is there a way to go about this? 

public PXProcessing<SOShipment, Where<SOShipment.operation,, And<Where<SOShipmentExt.usrToTransfer, IsNull, Or<SOShipmentExt.usrToTransfer.IsEqual<False>>>>>> shipments;

SQL:

select * from SOShipment
where Operation = 'R' and 
(UsrToTransfer is null or UsrToTransfer = 0)

Thanks,

Adam