diff --git a/10-seq-hacking/vector_v5.py b/10-seq-hacking/vector_v5.py
@@ -187,6 +187,65 @@
    '<4.000e+00, 1.047e+00, 9.553e-01, 7.854e-01>'
    >>> format(Vector([0, 1, 0, 0]), '0.5fh')
    '<1.00000, 1.57080, 0.00000, 0.00000>'
"""

from array import array
@@ -228,10 +287,10 @@ def __hash__(self):
        return functools.reduce(operator.xor, hashes, 0)

    def __abs__(self):
-        return math.sqrt(sum(x * x for x in self))

    def __bool__(self):
-        return bool(abs(self))

    def __len__(self):
        return len(self._components)
@@ -268,16 +327,30 @@ def angle(self, n):  # <2>
    def angles(self):  # <3>
        return (self.angle(n) for n in range(1, len(self)))

    def __format__(self, fmt_spec=''):
        if fmt_spec.endswith('h'):  # hyperspherical coordinates
            fmt_spec = fmt_spec[:-1]
-            coords = itertools.chain([abs(self)],
-                                     self.angles())  # <4>
            outer_fmt = '<{}>'  # <5>
        else:
-            coords = self
            outer_fmt = '({})'  # <6>
        components = (format(c, fmt_spec) for c in coords)  # <7>
        return outer_fmt.format(', '.join(components))  # <8>

    @classmethod