 Linnebo thus contrasts abstract objects, which are thin and have a shallow nature, with concrete objects, which do not have a shallow nature. Linnebo extends this view in several ways. He constructs an account of mathematical objects that goes beyond the way of abstraction principles by providing a reconstruction of set theory in terms of ‘dynamic abstraction’ (2018, ch. 3). This form of minimalism also allows for abstract objects of a mixed nature; namely, those that are thin relative to other objects. For example, the type of the letter ‘A’ is abstract because it is thin and has a shallow nature, but it is thin with respect the tokens of the letter ‘A’.