X. serves in this Art to inquire into particular issues in any science through affirmation and negation, with and without a medium. This is because X. is a figure made of opposites in order to receive likenesses or unlikenesses of A. as well as likenesses or unlikenesses of all things in all sciences and in whatever the human intellect can grasp, in the same way that a straight mirror reflects true images and a crooked mirror reflects distorted images since it receives them in a distorted way. And this is what the author of this Art intended when writing the propositions of X.