Barrow and Leibniz on the fundamental theorem of the calculus

In 1693, Gottfried Whilhelm Leibniz published in the Acta Eruditorum a geometrical proof of the fundamental theorem of the calculus. During his notorious dispute with Isaac Newton on the development of the calculus, Leibniz denied any indebtedness to the work of Isaac Barrow. But it is shown here, that his geometrical proof of this theorem closely resembles Barrow’s proof in Proposition 11, Lecture 10, of his Lectiones Geometricae, published in 1670.