Compatibility rules inside a product promotion

Hi,

in my project i need to apply some compatibility rules between products in a product promotion. For example, I have a promotion which have a product 1 and 2 with min=1,max=1 and defaut=1. Then I have a product 3 and 4 inside the product promotion that are not obligatory, which means their configuration is min=0,max=1,default=1. But now i want to create a rule which specifies that, if in buy the product 3 inside this promotion, i should not be able to buy product 4 and otherwise. I couldn't find a way to this this job. I already know about compatibility