Get started on a lattice instance for naturals.

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

Lattice.agda

@@ -153,3 +153,14 @@ private module NatInstances where
             ; ⊔-least = min-greatest
             }
         }
+
+    NatLattice : Lattice ℕ
+    NatLattice = record
+        { _≼_ = _≤_
+        ; _⊔_ = _⊔_
+        ; _⊓_ = _⊓_
+        ; isLattice = record
+            { joinSemilattice = Semilattice.isSemilattice NatMaxSemilattice
+            ; meetSemilattice = Semilattice.isSemilattice NatMinSemilattice
+            }
+        }