how to declare a local variable in custom pll files of oracle ebs?

how to declare a local variable to copy a item value from one record to other record

(i use form builder 6i )

i try to use a global variable by :

defult_value(' ', 'GLOBAL.a');
copy(name_in('block_name.item_name'), 'GLOBAL.a');

but i use a multiforms and i need a local variable to each form.