What does a number look like? What's a (natural) number?
We represent numbers with symbols like 1, 2, 3, I, II, III. We are aware of objects that have a numeric property: A square has 4 sides.
But, what about the number itself? What is it? What does it look like?
In 1923, John von Neumann proposed a set-theoretic construction of natural numbers: We can start with the empty set, and then define the next number as the set containing all previous numbers:
0 = {} 1 = { {} } 2 = {0, 1} = { {}, {{}} }, 3 = {0, 1, 2} = { {}, {{}}, { {}, {{}} } } And so on.
Numbers, is a collection inspired by von Neumann's construction: In each work, closed shapes correspond to sets.