problem with image button

Hi there, Let's say I have a form with three image buttons: <input type=image name=add src="add.gif"> <input type=image name=delete src="delete.gif"> <input type=image name=update src="update.gif"> when I process the form I want to see what button was pressed, but instead of add being set, add.x and add.y get set. now the question is: what's the best way to check which one is set since doing this: if(isset($add.x)) ... gives a parse error? thanks, - Mark