code: def concat(self, tailvec):
          '''Returns the result of concatenating tailvec to the implicit
          parameter'''
          newvec = ImmutableVector()
          vallist = [(i + self._length, tailvec[i]) \
                  for i in range(0, tailvec._length)]
          newvec.tree = self.tree.multi_assoc(vallist)
          newvec._length = self._length + tailvec._length
          return newvef concat(self, tailvec):
          '''Returns the result of concatenating tailvec to the implicit
          parameter'''
          newvec = ImmutableVector()
          vallist = [(i + self._length, tailvec[i]) \
                  for i in range(0, tailvec._length)]
          newvec.tree = self.tree.multi_assoc(vallist)
          newvec._length = self._length + tailvec._length
          return newvec
docs: Returns the result of concatenating tailvec to the implicit
          parameter