doc-src/IsarAdvanced/Classes/Thy/code_examples/Classes.hs

 
 class (Classes.Semigroup a) => Monoidl a where {
   neutral :: a;
 };
 
-class (Classes.Monoidl a) => Group a where {
+class (Classes.Monoidl a) => Monoid a where {
+};
+
+class (Classes.Monoid a) => Group a where {
   inverse :: a -> a;
 };
 
 inverse_int :: Integer -> Integer;
 inverse_int i = negate i;

 
 instance Classes.Monoidl Integer where {
   neutral = Classes.neutral_int;
 };
 
+instance Classes.Monoid Integer where {
+};
+
 instance Classes.Group Integer where {
   inverse = Classes.inverse_int;
 };
 
-pow_nat :: (Classes.Group b) => Classes.Nat -> b -> b;
+pow_nat :: (Classes.Monoid a) => Classes.Nat -> a -> a;
 pow_nat (Classes.Suc n) x = Classes.mult x (Classes.pow_nat n x);
 pow_nat Classes.Zero_nat x = Classes.neutral;
 
 pow_int :: (Classes.Group a) => Integer -> a -> a;
 pow_int k x =