Description: Define the covers relation (on the Hilbert lattice). Definition 3.2.18
of PtakPulmannova p. 68, whose notation we use. Ptak/Pulmannova's
notation A 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 cvbr and cvbr2 for membership
relations. (Contributed by NM, 4-Jun-2004)(New usage is discouraged.)