EX12: This example gives some simple headings and demonstrates heading name
      inheritance.

@O@<ex12.out@>==@{dummy text@}

@A@<Feed the Penguins and Save the World@>
@B@<Feed the Penguins@>
@C@<Feed the little penguins@>
@C@<Feed the big penguins@>
@B@<Save the World@>
@C@<Save Europe@>
@C@<Save Africa@>

@C This heading hasn't been given an explicit name, but will inherit the
name \p{Save the rest of the world} from the macro definition below.

@$@<Save the rest of the world@>@Z==@{...@}