  What would you do if you were asked to "add" knowledge? Would you say that
"one plus one knowledge" is two "knowledges"? Less than that? More? Or
something in between? Adding knowledge sounds strange, but it brings to the
forefront questions that are as fundamental as they are eclectic. These are
questions about the nature of knowledge and about the use of mathematics to
model reality. In this chapter, I explore the mathematics of adding knowledge
starting from what I believe is an overlooked but key observation: the idea
that knowledge is non-fungible.
