R' Akiva stated three things; concerning two [the Sages] agreed with him, and concerning one they did not agree with him. Concerning a lime-worker's sandal [the Sages agreed] that it is suscept-ible to the tumah of midras.  [And the Sages also agreed with R' Akiva] con-cerning the remnants of an oven [that they must be at least] four [tefachim in size]. For [the Sages] used to say that three tefachim was sufficient, but they conceded to [R' Akiva].  And concerning one they did not agree with him, [namely,] concerning a chair from which two of its [seat] slats were removed, one next to the other, which R' Akiva declares susceptible to tumah contamination, but the Sages declare it not susceptible to tumah contamination.