hello odoo community

I have a button in purchase requestion form, it's visible in states of "in_progress" for group1 and group 2 but I want invisible this button if one user of group2 creates purchase requestion in other words I don't want a user to approve his own request

how can I do that?

<button groups="group1,group2" name="tender_done" states="in_progress" string="Done" type="object" icon="gtk-jump-to" />

openerp V6