begin
  if    :blk.name <> :blk.old_name
     or :blk.address1 <> :blk.old_address1
     or :blk.phone <> :blk.old_phone
     or :blk.city <> :blk.old_city then
    insert into prev_addr
                (name, address1, phone,
                 city)
         values (:blk.old_name, :blk.old_address1, :blk.old_phone,
                 :blk.old_city);
  end if;
end;