"When opened, a book shows mirror symmetry. Its axis is the spine, around which the pages are turned. Thus any typographic approach, including an asymmetric one, has always to take account of the symmetry that is inherent in the physical object of a book. The axis of symmetry of the spine is always there; one can certainly work over it, but not deny it. In this respect book typography is essentially different from the typography of single sheets, as in business printing, posters, and so on."
— HOCHULI, Jost & KINROSS, Robin. Designing books: practice and theory. Hyphen Press. London,1996. p.35