where clause and over-ride whichever methods you please.
+<Sect2> <Title> Using generics </Title>
+</Sect2>
+<Para>
+To use generics you need to
+<ItemizedList>
+<ListItem>
+Use the <Option>-fgenerics</Option> flag.
+</ListItem>
+<ListItem>
+Import the module <Literal>Generics</Literal> from the <Literal>lang</Literal> package.
+This import brings into scope the data types <Literal>Unit</Literal>, <Literal>:*:</Literal>,
+and <Literal>:+:</Literal>. (You don't need this import if you don't mention these
+types explicitly; for example, if you are simply giving instance declarations.)
+</ListItem>
+</ItemizedList>
+
<Sect2> <Title> Changes wrt the paper </Title>
<Para>
Note that the type constructors <Literal>:+:</Literal> and <Literal>:*:</Literal>