A bin whose upper [part] was removed is tamei on account of the lower [part]. [If] the lower [part] was removed, it is tamei on account of the upper [part]. [If both] the upper and lower [parts] were removed, R’ Yehudah rules [it] tamei on account of the sides, but the Sages rule [it] tahor. A stonemason’s seat [can become] tamei with midras [tumah].