At first glance, the concept of equality in maths seems unambiguous. Denoted by two parallel lines, the equals sign looks elegant, simple and entirely black and white. But between those two lines lies a grey area, a world of flexibility, creativity and innovation.And once you see this nuance, you quickly realise that sameness and difference, equality and inequality, are not nearly as immutable as they may seem. In fact, they are the opposite: a mathematical playground of choice and abstraction, leading to far greater insight than you could have dreamed. In UnEqual, Mathematician Eugenia Cheng explores the rich and rewarding world of the interplay between sameness and difference, from numbers to manifolds to category theory and beyond.