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 _____      ______   ______    __   __    _  _   
|  __ \\   /_   _// |      \\  \ \\/ //  | \| || 
| |  \ ||   -| ||-  |  --  //   \ ` //   |  ' || 
| |__/ ||   _| ||_  |  --  \\    | ||    | .  || 
|_____//   /_____// |______//    |_||    |_|\_|| 
 -----`    `-----`  `------`     `-`'    `-` -`

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Text this: Normalisers of subgroups of the modular group