AN ACT AUTHORIZING GOVENMENT EMPLOYEES WHO RETIRE UNDER REPUBLIC ACT NO. 660 OR PRESIDENTIAL DECREE NO. 1146 TO RECEIVE, IN ADDITION TO THE LUMP SUM ANNUITY FROM THE GOVERNMENT SERVICE INSURANCE SYSTEM, THE DIFFERENCE BETWEEN THE ANNUITY AND THE TOTAL AMOUNT THEY SHALL RECEIVE UNDER REPUBLIC ACT NO. 1616 WHICH SHALL BE PAID BY THEIR EMPLOYER