'Return the *i* th token in the corpus file underlying this
corpus view.  Negative indices and spans are both supported.'

def __getitem__(self, i):

    if isinstance(i, slice):
        (start, stop) = slice_bounds(self, i)
        return LazySubsequence(self, start, stop)
    else:
        if (i < 0):
            i += len(self)
        if (i < 0):
            raise IndexError('index    out    of    range')
        try:
            return next(self.iterate_from(i))
        except StopIteration:
            raise IndexError('index    out    of    range')
