stiffest possible infill

This could be used as an infill for 3D printed parts.

It is a superposition of simple cubic infill with an
octahedral infill (octet truss with filled in faces) of halve the size.
A "cubic-octahedral" infill - so to say.

**It comes from this paper:**
"Mechanical metamaterials at the theoretical limit of isotropic elastic stiffness".
https://www.nature.com/articles/nature21075
doi: 10.1038/nature21075

The orientation is here chosen such, that
no planes are coplanar to the printbed.