Komentarz do Negaim 13:6

בית שהוא מיסך על גבי בית המנוגע – as for example, that the house that is certified as leprous is built within another house. And similarly, a tree that the leprous house is built underneath it.

If a house overshadowed a house with a nega and so also if a tree overshadowed a house with a nega, anyone who enters the outer [of the two] remains clean, the words of Rabbi Elazar ben Azariah. This mishnah discusses a house that overshadows another house with a nega or a tree that overshadows a house with a nega. According to Rabbi Elazar ben Azariah one who enters the outer house or goes under the tree, meaning the structure that overshadows, is not impure.

הנכנס לחיצון טהור – for this one stands alone and that one stands alone. And it is similar to a house and the upper story, for if leprosy is in the house, the upper story is pure.

Rabbi Eliezer said: if one stone of it causes uncleanness by entering, should not the house itself cause uncleanness by entering? Rabbi Eliezer disagrees, drawing a sort of "a fortiori" argument. If the impurity of an afflicted house is strong enough that if one enters the house he is impure, then all the more so it should cause one who enters an "ohel," an overshadowing structure, to be impure.

ומה אם אבן אחת – that is from the house with leprosy, which defiles all that is in the tent.

הבית כולו – that is underneath another house, all the more so that it would defile all that is within the outer house. And the Halakha is according to Rabbi Eliezer (see also Tractate Negaim, Chapter 11, Mishnah 6).