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Indikatorelemente, insbesondere pH-Indikatoren für alle Typen der Mund-Nasen-Bedeckung, deren Aufgabe es ist, die Wechselnotwendigkeit in genutzten Masken durch Verfärbung dauerhaft anzuzeigen
G. Davis, Polyhymnia: The Rhetoric of Horatian Lyric Discourse. Berkeley: University of California Press, 1991. Pp. xi+ 282. ISBN 0-520-07077-1. $39.95.