Description: Define the covering relation for subspaces of a left vector space.
Similar to Definition 3.2.18 of PtakPulmannova p. 68.
Ptak/Pulmannova's notation A ( W ) B is read " B covers
A " or " A is covered by B " , and it means that B is
larger than A and there is nothing in between. See lcvbr for
binary relation. ( df-cv analog.) (Contributed by NM, 7-Jan-2015)