New views that are introduced with the new
version of Nat:

1) in RelationsAndOrders:

view ExtTotalOrder_in_Nat:
          RichTotalOrder to Nat =
          sort Elem |-> Nat,
          ops inf |-> min,
                 sup |-> max
end

2) in Algebra I:

view CommutativeMonoid_in_Nat_Add:
         CommutativeMonoid to Nat =
         sort Elem |-> Nat,
         ops e |-> 0, __ * __ |-> __ + __
end

view ExtCommutativeMonoid_in_Nat_Mult:
RichCommutativeMonoid to Nat =
sort Elem |-> Nat, ops e |-> 1, __ * __ |-> __ * __
end