[Bug libstdc++/58562] std::sort fails with -D_GLIBCXX_DEBUG enabled, whose bug?

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58562

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Specifically it fails this requirement:

matrixVectorProdTerm a(1, 0, 0);
matrixVectorProdTerm b(0, 1, 0);

assert( !(a<b && b<a) );

i.e. with your definition of ordering two objects can both be less than each
other, which makes the ordering unsuitable for std::sort (or pretty much
anything else in the standard library that cares about sorting.)