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A equals left curly bracket x colon negative 1 less or equal than x less or equal than 1 right curly bracket. f colon A not stretchy rightwards arrow A defined by f left parenthesis x right parenthesis equals x vertical line x vertical linetext  Then  end text f text  is  end text

  1. a bijection
  2. an injection but not surjection
  3. a surjection but not an injection
  4.  neither an injection nor a surjection

The correct answer is: a bijection

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