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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 is_token_annotation_tier(self, tier):
 """ returns True, iff all events in the given tier annotate exactly one token. """

        for i, event in enumerate(tier.iter('event')):
            if self.indexdelta(event.attrib['end'], event.attrib['start']) != 1:
                return False
        return True