Oops, had debugging on.  On a proper linux workstation, the numbers are more like this:

Search size 2E5:

naive:            0.18-0.20s
lvish1 -N1:       0.80s
lvish1 -N4 -A20M: 0.36s

With no proper treatment of saturation, LVish is allocating 1.8GB whereas
naive is allocating 0.61 GB.

Next step is to drop saturated worlds from the ISet.  The step after that
is to cancel threads associated with failed worlds.