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  _____      ___     _    _    _    _    __   _   
 / ____||   / _ \\  | \  / || | || | || | || | || 
/ //---`'  | / \ || |  \/  || | || | || | '--' || 
\ \\___    | \_/ || | .  . || | \\_/ || | .--. || 
 \_____||   \___//  |_|\/|_||  \____//  |_|| |_|| 
  `----`    `---`   `-`  `-`    `---`   `-`  `-`

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Text this: Nonstationary panels with unobserved heterogeneity