Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
In many situations it is desirable to consider two group elements the same if they differ by an element of a given subgroup. For example, in D4 above, once a reflection is performed, the square never gets back to the r2 configuration by just applying the rotation operations (and no further reflections), i.e. the rotation operations are irrelevant to the question whether a reflection has been performed. Cosets are used to formalize this insight: a subgroup H defines left and right cosets, which can be thought of as translations of H by arbitrary group elements g. In symbolic terms, the left and right cosets of H containing g are
When are two group elements considered different?
A: unanswerable

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Greater London's population declined steadily in the decades after the Second World War, from an estimated peak of 8.6 million in 1939 to around 6.8 million in the 1980s. The principal ports for London moved downstream to Felixstowe and Tilbury, with the London Docklands area becoming a focus for regeneration, including the Canary Wharf development. This was borne out of London's ever-increasing role as a major international financial centre during the 1980s. The Thames Barrier was completed in the 1980s to protect London against tidal surges from the North Sea.
When was construction on the Thames Barrier completed?
A: the 1980s

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Hannover 96 (nickname Die Roten or 'The Reds') is the top local football team that plays in the Bundesliga top division. Home games are played at the HDI-Arena, which hosted matches in the 1974 and 2006 World Cups and the Euro 1988. Their reserve team Hannover 96 II plays in the fourth league. Their home games were played in the traditional Eilenriedestadium till they moved to the HDI Arena due to DFL directives. Arminia Hannover is another very traditional soccer team in Hanover that has played in the first league for years and plays now in the Niedersachsen-West Liga (Lower Saxony League West). Home matches are played in the Rudolf-Kalweit-Stadium.
What is the name of the stadium that the Hanover football team plays in?
A: HDI-Arena

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Glacial bodies larger than 50,000 km2 (19,000 sq mi) are called ice sheets or continental glaciers. Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces. The only extant ice sheets are the two that cover most of Antarctica and Greenland. They contain vast quantities of fresh water, enough that if both melted, global sea levels would rise by over 70 m (230 ft). Portions of an ice sheet or cap that extend into water are called ice shelves; they tend to be thin with limited slopes and reduced velocities. Narrow, fast-moving sections of an ice sheet are called ice streams. In Antarctica, many ice streams drain into large ice shelves. Some drain directly into the sea, often with an ice tongue, like Mertz Glacier.
What are glaciers smaller it in 50,000 km² called?
A:
unanswerable