the algebra of dependent types

TIL (or this week-ish I learned) why big-sigma and big-pi turn up in the notation of dependent type theory. I’ve long been aware of the zoo of more obscure Greek letters that turn up in papers about type system features of functional programming languages, μ , Λ , Π , Σ . Their meaning is usually clear from context but the reason for the choice of notation is usually not explained. I recently…