refactor(library/init/nat): make \nat notation available at top level

library/data/int/div.lean

@@ -11,7 +11,6 @@ import data.int.order data.nat.div
 open [coercions] [reduce-hints] nat
 open [declarations] nat (succ)
 open eq.ops
-notation `ℕ` := nat
 
 namespace int
 

library/init/nat.lean

@@ -7,9 +7,10 @@ prelude
 import init.wf init.tactic init.num
 open eq.ops decidable or
 
-namespace nat
 notation `ℕ` := nat
 
+namespace nat
+
   /- basic definitions on natural numbers -/
   inductive le (a : ℕ) : ℕ → Prop :=
   | refl : le a a