“Subjects who reciprocally recognize each other as such, must consider each other as identical, insofar as they both take up the position of subject; they must at all times subsume themselves and the other under the same category. At the same time, the relation of reciprocity of recognition demands the non-identity of one and the other, both must also maintain their absolute difference, for to be a subject implies the claim of individuation.”

Interview on National Public Radio (13 December 1974)
Context: I think politicians and movie actors and movie executives are similar in more ways than they’re different. There is an egocentric quality about both; there is a very sensitive awareness of the public attitude, because you live or die on public favor or disfavor. There is the desire for publicity and for acclaim, because, again, that’s part of your life... And in a strange and bizarre way, when movie actors come to Washington, they’re absolutely fascinated by the politicians. And when the politicians go to Hollywood, they’re absolutely fascinated by the movie stars. It’s a kind of reciprocity of affection by people who both recognize in a sense they’re in the same racket.

As quoted by Thomas Little Heath, Diophantos of Alexandria: https://books.google.com/books?id=ABkPAAAAIAAJ A Study in the History of Greek Algebra (1885)
Arithmetica (c. 250 AD)

§ 3.
Linear Associative Algebra (1882)
Context: All relations are either qualitative or quantitative. Qualitative relations can be considered by themselves without regard to quantity. The algebra of such enquiries may be called logical algebra, of which a fine example is given by Boole.
Quantitative relations may also be considered by themselves without regard to quality. They belong to arithmetic, and the corresponding algebra is the common or arithmetical algebra.
In all other algebras both relations must be combined, and the algebra must conform to the character of the relations.

Source: Jean-Jacques Rousseau: Restless Genius (2005), Ch. 18 : Rousseau the Controversialist: Émile and The Social Contract.

Selected Readings from the Works of Mao Tse-Tung, pp. 121
On Contradiction (1937)
Original: (zh-CN) 一切矛盾着的东西，互相联系着，不但在一定条件之下共处于一个统一体中，而且在一定条件之下互相转化，这就是矛盾的同一性的全部意义。列宁所谓“怎样成为同一的（怎样变成同一的），——在怎样的条件之下它们互相转化，成为同一的”，就是这个意思。

Source: The Limits of Evolution, and Other Essays, Illustrating the Metaphysical Theory of Personal Ideaalism (1905), Preface to First Edition, p.xiii

Source: The Science of Rights 1796, P. 173-175

Ego and Non-Ego
The Note-Books of Samuel Butler (1912), Part XX - First Principles