Scriptor in the Vatican Library (1958–88), and author of numerous valuable studies on Syriac and Christian Arabic literature. His books include a bibliography of oriental liturgical rites, covering 1900–60 (1962), a pioneering study of Melkite synaxaria (Subsidia Hagiographica 45, 1969), two monographs on mss. in the Borgia collection (Syr. 39: SeT 292, 1981; and Syr. 60, a Gazza: SeT 326, 1987), and a study of an Arabic translation of the Saying of the Fathers in the Paradise of ʿEnanishoʿ (CSCO 495, 1987).