Sukkah 20B

שהן טמאות, ושל טבריא שהן טהורות. על מה נחלקו? על שאר מקומות. מר סבר: כיון דליכא דיתיב עלייהו ⁠— כדטבריא דמיין, ומר סבר: כיון דמקרי ויתבי עלייהו ⁠— כדאושא דמיין.

that they can become ritually impure, even with impurity imparted by treading, as those mats are produced for the purpose of lying upon them. And they also agreed concerning the coarse mats of Tiberias, that they are ritually pure, as these are produced exclusively for use in partitions and for roofing. Concerning what mats do they disagree? It is concerning the mats produced in the rest of the places. One Sage, i.e., the Rabbis, holds: Since there is no one who sits on these mats regularly, they are comparable to the mats of Tiberias and are pure. And one Sage, R' Dosa, holds that since it happens and one sits on them on occasion, they are comparable to the mats of Usha and are impure.

אמר מר: כל החוצלות מטמאין טמא מת, דברי רבי דוסא. והתניא: וכן היה רבי דוסא אומר כדבריו!

The Talmud analyzes the Mishnah cited above. The Master said: All types of ḥotzalot can become ritually impure with impurity imparted by a corpse; this is the statement of R' Dosa. Apparently, they are all considered vessels, which is why they are susceptible to ritual impurity and one may not roof the sukka with them. The Talmud asks: But wasn’t it taught in the baraita: And likewise, R' Dosa would say in accordance with his statement, i.e., in accordance with the statement of R' Yishmael, son of R' Yosei, in the name of his father, that all types of mats are ritually pure, and one may roof a sukka with them? Don’t these two sources contradict each other?

לא קשיא: הא דאית ליה גדנפא, הא דלית ליה גדנפא.

The Talmud answers: This is not difficult. This Mishnah is referring to a mat that has an upturned edge, which renders the mat a vessel susceptible to ritual impurity. That baraita is referring to a mat that does not have an upturned edge [gedanpa]; therefore, it is not a vessel and is not susceptible to impurity.