CREATE TABLE Ref_Shipping_Agents (document_id VARCHAR, document_status_code VARCHAR, document_type_code VARCHAR)
CREATE TABLE Documents (document_id VARCHAR, document_status_code VARCHAR, document_type_code VARCHAR)

List document id of documents status is done and document type is Paper and the document is shipped by shipping agent named USPS.
SELECT document_id FROM Documents WHERE document_status_code = "done" AND document_type_code = "Paper" INTERSECT SELECT document_id FROM Documents JOIN Ref_Shipping_Agents ON Documents.shipping_agent_code = Ref_Shipping_Agents.shipping_agent_code WHERE Ref_Shipping_Agents.shipping_agent_name = "USPS"
SELECT "document_id" FROM "Documents" WHERE "Paper" = "document_type_code" AND "document_status_code" = "done" INTERSECT SELECT "document_id" FROM "Documents" JOIN "Ref_Shipping_Agents" ON "Documents"."shipping_agent_code" = "Ref_Shipping_Agents"."shipping_agent_code" AND "Ref_Shipping_Agents"."shipping_agent_name" = "USPS"