Phenomenology of Spirit, Preface, paragraph 43

In mathematical cognition, insight is a function external to the matter; it follows from this that the true matter is thereby altered. The means, construction, and proof, contain, no doubt, true propositions; but all the same it must be said that the content is false. The triangle in the above example is taken to pieces, and its parts beaten into other figures to which the construction in the triangle gives rise. It is only at the end that the triangle, which was the important thing, is restored, which was lost sight of in the course of the construction, and which seemed to be only fragments belonging to other wholes. Here we see negativity of content entering as well, which must be termed a falsity just as much as is, in the case of the movement of the concept, the disappearance of thoughts taken to be fixed.