Three Dialogues between Hylas and Philonous by George Berkeley: “His _Three Dialogues between Hylas and Philonous, in Opposition to Sceptics and Atheists_, undertake to prove that there is no such thing as matter at all, and that the world consists of nothing but minds and their ideas.”
An Introduction to Mathematics by Alfred North Whitehead: “(1) Cf. A. N. Whitehead, _Introduction to Mathematics_ (Home University Library).”
The Republic by Plato: “Plato: _Republic_, especially Books VI and VII.”