I must say that I’m intrigued by Julia type system and I want to understand it more. In particular I want to understand works like this of prof. Jan Vitek and his collaborators mentioned in his 2021 JuliaCon keynote and newer papers like _ Decidable Subtyping of Existential Types for Julia_ published in 2023, but I lack a background for it, so I want to ask for help. What material should I studied to get into this topic? I assume I should now some solid type theory, but I don’t know where to start.

I’m person that is very found of logic, mathematical logic and math in general, so I would prefer resources that emphasis rigour and formal structures, not something that is easy for beginners. Even if this first route cost me more sweet, I strongly believe that I will gain much more from it. At this moment price of books and related materials is secondary thing to me, quality is the most important factor.