To express the class, not-X, that is, the class including all individuals that are not Xs. The class X and the class not-X together make the Universe. But the Universe is 1, and the class X is determined by the symbol x, therefore the class not-X will be determined by the symbol 1 − x. Hence the office of the symbol 1 − x attached to a given subject will be, to select from it all the not-Xs which it contains.
