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)

Lattice/Prod.agda

@@ -1,11 +1,12 @@
 open import Lattice
 
-module Lattice.Prod {a} {A B : Set a}
-    (_≈₁_ : A → A → Set a) (_≈₂_ : B → B → Set a)
+module Lattice.Prod {a b} {A : Set a} {B : Set b}
+    (_≈₁_ : A → A → Set a) (_≈₂_ : B → B → Set b)
     (_⊔₁_ : A → A → A) (_⊔₂_ : B → B → B)
     (_⊓₁_ : A → A → A) (_⊓₂_ : B → B → B)
     (lA : IsLattice A _≈₁_ _⊔₁_ _⊓₁_) (lB : IsLattice B _≈₂_ _⊔₂_ _⊓₂_) where
 
+open import Agda.Primitive using (Level) renaming (_⊔_ to _⊔ℓ_)
 open import Data.Nat using (ℕ; _≤_; _+_; suc)
 open import Data.Product using (_×_; Σ; _,_; proj₁; proj₂)
 open import Data.Empty using (⊥-elim)
@@ -35,7 +36,7 @@ open IsLattice lB using () renaming
     ; ≺-cong to ≺₂-cong
     )
 
-_≈_ : A × B → A × B → Set a
+_≈_ : A × B → A × B → Set (a ⊔ℓ b)
 (a₁ , b₁) ≈ (a₂ , b₂) = (a₁ ≈₁ a₂) × (b₁ ≈₂ b₂)
 
 ≈-equiv : IsEquivalence (A × B) _≈_