"Ainsi, les pivots et les autorités sont les types distincts de pages qui montrent une forme normale de la symbiose: un bon pivot se dirige à beaucoup de bonnes autorités, alors qu'une bonne autorité est dirigée à par beaucoup de bons pivots" Warning - machine translation ;)
An authority page has two features - 1) that the content is good (this is ultimately judged by a human for a core set of authority pages - eg by pinching a few from the ODP) and 2) that several good hub pages link to it.
A hub page has one feature - that it links to several good authority pages.
As can be seen, this is a bit of a circular argument if you consider pages in isolation. However, it really is just a set of several hundred simultaneous equations (bit of revision needed here for the Artists) in several hundred unknowns, and can be solved with matrix methods.
I say 'just a set of several hundred simultaneous equations' but it mustn't be forgotten that a famous aircraft designer of the early twentieth century spent 6 months solving a set of 70 equations in 70 unknowns by hand. The thing could now be done on a PC in the twinkling of an eye. Is the web still the greatest achievement of the electron?