Try to generalize universe levels where possible

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

Lattice/IterProd.agda

@@ -1,5 +1,9 @@
 open import Lattice
 
+-- Due to universe levels, it becomes relatively annoying to handle the case
+-- where the levels of A and B are not the same. For the time being, constrain
+-- them to be the same.
+
 module Lattice.IterProd {a} {A B : Set a}
     (_≈₁_ : A → A → Set a) (_≈₂_ : B → B → Set a)
     (_⊔₁_ : A → A → A) (_⊔₂_ : B → B → B)