What would be easier to accomplish is to have two fields, an include and exclude field. Then the results query can get posts in one category that do not have the other category. This is simpler and more straight forward than trying to difference the posts of two different pages, yet you end up with the same results.

Or are you looking for XOR logic? Posts that have one category or the other, but not both? This too can be accomplished with two fields. The query is more complicated to setup, but still better than trying to work from other results pages.