k_mul() comments:  Explained why there's always enough room to subtract ah*bh and al*bl.  This is much easier than explaining why that's true for (ah+al)*(bh+bl), and follows directly from the simple part of the (ah+al)*(bh+bl) explanation.
k_mul() comments:  Explained why there's always enough room to subtract
ah*bh and al*bl.  This is much easier than explaining why that's true
for (ah+al)*(bh+bl), and follows directly from the simple part of the
(ah+al)*(bh+bl) explanation.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator