Kommentar zu Oholot 15:2

טבליות של עץ – that are adjacent to one another and each of them are a handbreadth above the ground and touch at their corners – each other with its neighbor that is near it, and it is the manner of the corners of the boards that they are not a handbreadth wide, therefore, vessels that are underneath the first that the defilement is under it are impure, but that which is under the second are pure.

[With regard to] wooden tablets which touch each other at their corners, and are one handbreadth high off the ground: If there is uncleanness beneath one of them, [a person] touching the second [tablet] becomes defiled with seven-day defilement. Vessels under the first [tablet] become unclean; but those under the second remain clean. This section describes two wooden tablets that touch each other only at one corner. The part that is touching is less than one handbreadth. The two tablets are one handbreadth off the ground, the required amount to be an ohel. Although they are touching only at their corners, in some ways they are considered to be one ohel. Therefore, if there is uncleanness beneath one of them, a person who touches the other one is impure as if he had been in contact with a dead body. This is where it gets a bit tricky. If there are vessels underneath the tablets, those under the one where the corpse uncleanness is found are defiled, but those under the other one are not. This seems to contradict the previous line. Albeck explains that since the impurity is not under the second tablet and the second tablet is not touching the first tablet by an amount the size of a handbreadth, the impurity doesn't spread beneath it. However, we do look at the tablet as if it was overhanging the impurity and one who touches it is impure.

הנוגע בשניה טמא טומאת שבעה – and even though it is taught in the Mishnah in the first chapter [Mishnah 2] that: “Utensils which touch the corpse and utensils [which touch other] utensils are unclean with the uncleanness of seven [days]. The third, whether man or utensils, is unclean with the uncleanness [that passes at] evening.” But it is taught in the Mishnah there (i.e., at the conclusion of Mishnah 3): “The tent does not come under consideration.” Therefore, the board that the defilement is underneath it is not part of the count (i.e., is not included).

A table does not bring uncleanness unless it contains a square of at least one handbreadth. Tables were often expanded by adding squares, one next to the other, in order to allow more guests (like the leafs we add to our tables). If there is no single square that is at least one handbreadth square, meaning one square to serve as the base of the table, then none of the squares join to form an ohel. This is not considered to be a sustainable ohel (for this concept see 8:5).

עד שיהא בו ריבוע בפותח טפח (until it has a squared handbreadth) – it is a kind of breached/broken-through chest that has four walls that they would make for a table when the table sits upon it, and that breached chest is called a square. And sometimes, that the table protrudes and extends outside from that square a handbreadth or less or more, and now it states that it needs that the table protrudes outward from that square with an opening of handbreadth, for just as what is within the square does not combine, if defilement is also within the square from the inside, the square interposes and prevents the defilement from passing to the outside.