Derailleur gears several standards in use, and in each the product of the derailleur's actuation ratio and the length of cable pulled must equal the pitch of the rear sprockets. The following standards exist. Some rear derailleurs, especially for mountain bikes, incorporate a clutch to keep the lower length of chain in sufficient tension to prevent the chain from striking the bottom of the chain stay, called "chain slap", and which can damage the chain stay. Clutches are also helpful in preventing the chain from derailing from the chain ring on systems without a front derailleur. The front derailleur only has to
What Is a Nation? to the reasons based on race, geography, history and so on. They argue that Renan maintains his intellectual background but subtly, i.e. the arguments he explicitly used in "What is a Nation?" are not consistent with his thinking. The concept of "daily plebiscite" would be ambiguous. They argue that the definition is an opportunist idealization and it should be interpreted within the Franco-Prussian War and in the midst of the dispute concerning the Alsace-Lorraine region. What Is a Nation? "What is a Nation?" ("Qu'est-ce qu'une nation?") is an 1882 lecture by French historian Ernest Renan (1823–1892), known for the statements