Jacob Neusner: Is Scripture the origin of the Halakhah? (= Studies in Judaism). University Press of America, Lanham 2005, ISBN 0-7618-3117-7, S.141 (englisch, Vorschau in der Google-Buchsuche): “The pertinent classification of uncleanness called Midras- or pressure-uncleanness pertains only to objects that ordinarily are used to bear weight or pressure, that is, beds and chairs and things analogous to them.”
