Borghouts, J. F. (2010), Egyptian: an introduction to the writing and language of the Middle Kingdom, 2 vols. Egyptologische Uitgaven 24, page 108, note 1
Gardiner, Alan Henderson (1957), Egyptian grammar being an introduction to the study of hieroglyphs, 3rd, revised edition, page 497
Brovarski, E. (2018), Naga ed-Dêr in the First Intermediate Period., p. 305, Brovarski discusses the sign in its function as Old Kingdom classifier of jz "tomb"
Kuhlmann, Klaus P. (1977), Der Thron im alten Ägypten: Untersuchungen zu Semantik, Ikonographie und Symbolik eines Herrschaftszeichens. Abhandlungen des Deutschen Archäologischen Instituts Kairo, Ägyptologische Reihe 10, p. 75, Kuhlmann explains the sign form with steps as a combination of two stairs depicted from the side.
Cervelló-Autuori, Josep (2006), Cervelló-Autuori, Josep 2006. Les déterminatifs d'édifices funéraires royaux dans les Textes des Pyramides et leur signification sémantique, rituelle et historique. Bulletin de l'Institut Français d'Archéologie Orientale 106, 1-19, p. 14 and fig. 2-4
Hainline, Brendan (2023), Can tomb terminology be used as a criterion for dating the Pyramid Texts? Journal of Egyptian History 16 (1), 1-29, p. 8 & 13-15, Hainline discusses the sign variant O24A as classifier of ḥꜣ.t "tomb".
Lapp, Günther (1986), Die Opferformel des Alten Reiches: unter Berücksichtigung einiger späterer Formen. Sonderschrift, Deutsches Archäologisches Institut, Abteilung Kairo 21, p. 61 §99