Use records rather than nested pairs to represent 'fixed height'

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

Lattice/IterProd.agda

@@ -14,6 +14,7 @@ open import Agda.Primitive using (lsuc)
 open import Data.Nat using (ℕ; zero; suc; _+_)
 open import Data.Product using (_×_; _,_; proj₁; proj₂)
 open import Utils using (iterate)
+open import Chain using (Height)
 
 open IsLattice lA renaming (FixedHeight to FixedHeight₁)
 open IsLattice lB renaming (FixedHeight to FixedHeight₂)
@@ -44,10 +45,10 @@ private
             fhB : FixedHeight₂ h₂
 
         ⊥₁ : A
-        ⊥₁ = proj₁ (proj₁ (proj₁ fhA))
+        ⊥₁ = Height.⊥ fhA
 
         ⊥₂ : B
-        ⊥₂ = proj₁ (proj₁ (proj₁ fhB))
+        ⊥₂ = Height.⊥ fhB
 
         ⊥k : ∀ (k : ℕ) → IterProd k
         ⊥k = build ⊥₁ ⊥₂
@@ -58,7 +59,7 @@ private
             fixedHeight : IsLattice.FixedHeight isLattice height
             ≈-dec : IsDecidable _≈_
 
-            ⊥-correct : proj₁ (proj₁ (proj₁ fixedHeight)) ≈ ⊥
+            ⊥-correct : Height.⊥ fixedHeight ≈ ⊥
 
     record Everything (k : ℕ) : Set (lsuc a) where
         T = IterProd k