All that is wanting in his writings, especially in his Isagoge in artem analyticam (1591), in order to make them look like a modern school algebra, is merely the sign of equality - a want which is the more striking because Robert Recorde had made use of our present symbol for this purpose since 1 557, and Xylander had employed vertical parallel lines since 1575.
Under him Avicenna read the Isagoge of Porphyry and the first propositions of Euclid.
Joachim Jung, in his Isagoge phytoscopica (1678), recognized that the plant-body consists of certain definite members, root, stem and leaf, and defined them by their different form and by their mutual relations.
He translated into Latin Aristotle's Analytica Priora et Posteriora, the Topica, and Elenchi Sophistici; and he wrote commentaries on Aristotle's Categories, on his book lrEpi Epµnvcias, also a commentary on the Isagoge of Porphyrius.
C. Meiser (Leipzig, 1877), and on Porphyry's Isagoge, ed.