This would be more useful and more upvoteable if you had provided some text for context.
TLDR: If you interpret sum types as + and product types (tuples/structs/objects) as *, type definitions can be read as polynomials. Recursive type definitions, like for linked lists, can be read as recurrence equations. If you do some calculus over these things and compute the derivative of these type formulas, you get back something meaningful: The formula corresponding to the type's Zipper (https://en.wikipedia.org/wiki/Zipper_(data_structure)), a data structure for efficiently traversing and modifying functional data structures.
TLDR: If you interpret sum types as + and product types (tuples/structs/objects) as *, type definitions can be read as polynomials. Recursive type definitions, like for linked lists, can be read as recurrence equations. If you do some calculus over these things and compute the derivative of these type formulas, you get back something meaningful: The formula corresponding to the type's Zipper (https://en.wikipedia.org/wiki/Zipper_(data_structure)), a data structure for efficiently traversing and modifying functional data structures.
I like Chris Taylor's series of posts on this topic, as well as this shorter one: https://codewords.recurse.com/issues/three/algebra-and-calcu...