The meme "energy slave" sounds very not-PC and against the grain of current engineering best practice.
It's from the 1940s as was meant to remind people, depressed about the industrial age, that all of this power working for each of them, was also a potential source of higher living standards.
Without the exploitation of actual slaves. "Look ma! All these robots make life easier" (more household conveniences and appliances would come after the war).
This last one rounds out the Polyhedron class implementation, adding more subclasses in the concentric hierarchy.
