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

@@ -7,8 +7,9 @@ prelude
 import init.wf init.tactic init.num
 open eq.ops decidable or
 
+notation `ℕ` := nat
+
 namespace nat
-  notation `ℕ` := nat
 
   /- basic definitions on natural numbers -/
   inductive le (a : ℕ) : ℕ → Prop :=