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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def namedb_update_must_equal( rec, change_fields ):
 """ Generate the set of fields that must stay the same across an update. """

    
    must_equal = []
    if len(change_fields) != 0:
        given = rec.keys()
        for k in given:
            if k not in change_fields:
                must_equal.append(k)

    return must_equal