Sukkah 14 - July 21, 12 Av

Pictures Can one change the status of handles of items from being susceptible to impurity to not being susceptible to impurity by rendering it useless through one's thoughts or is it necessary to do an action? Can one use wooden boards for sechach? Did the rabbis forbid it as it looks like a ceiling and people may come to think they can use their house for a sukkah? Rabbi Meir and Rabbi Yehuda disagree. Rav and Shmuel disagree regarding the case in which Rabbi Meir and Rabbi Yehuda disagree - were they referring to boards that are four handbreadths wide, but all would agree that less than four handbreadths would be allowed? Or do they disagree regarding boards that are 3-4 handbreadths but ones that are four are forbidden by all? The gemara brings tannaitic sources and tries to see how they fit with Rav and Shmuel's opinions.