Here is what I wish to have:
Chapter 2 - Foo This is an introductory paragraph, spanning over the whole width of the document. This is the body of the | due to the use of the chapter which is written | 'book' class with the on two separate columns | 'twocolumn' option.
How can I achieve this layout?
Edit: I do not want to use multicol since it would be used on each chapter to explicitely specify what should be the default behaviour of my document (i.e. two columns). As such, the referenced question is not a duplicate.