select distinct paper from paper_master,printsize_master,stamps where stamps.paper_code=paper_master.paper_code and paper_master.paper<>' '  and year(stamps.issue_date)=1966 and month(issue_date)=4  and stamps.serial_no=\'0531\'  and printsize_master.printsize_code=stamps.printsize_code and printsize_master.printsize=\'2.99 x 2.1\'  order by paper