Alley may be paved, or unpaved, and a blind alley is a cul-de-sac. Modern urban developments may also provide a service road to allow for waste collection, or rear access for fire engines and parking. Because of geography, steps (stairs) are the predominant form of alley in hilly cities and towns. This includes Quebec City in Canada and in the United States Pittsburgh (see Steps of Pittsburgh), Cincinnati (see Steps of Cincinnati), Minneapolis, Seattle, and San Francisco as well as Hong Kong, Genoa and Rome. Some alleys are roofed because they are within buildings, such as the traboules of Lyon, or
Letter on the Blind people associated with the "Encyclopedia" led to his liberation after few months. Letter on the Blind In Letter on the Blind for the Use of those who can see (French: Lettre sur les aveugles à l'usage de ceux qui voient), Denis Diderot takes on the question of visual perception, a subject that, at the time, experienced a resurgence of interest due to the success of medical procedures that allowed surgeons to operate on cataracts (demonstrated in 1747 by Jacques Daviel) and certain cases of blindness from birth. Speculations were then numerous upon what the nature and use of vision was,