Related על תרומות 3:5

One who says, "The terumah for this pile [of produce] is in the north," then [the result would be that] the entire half nearest the north is rendered a medummah (a forbidden mixture of terumah and chullin), the words of Rebbi. But the Sages say, [what he can do instead] is arrange the pile in the form of the letter "chi" (similar to an X, to minimize contact between terumah and chullin). Rabban Shimon ben Gamaliel says, he can take the terumah from the northernmost [part].