Fuses the lists. A list's items are in its own rank order, best first; an item twice in one list counts once, at its
better rank. Every option is checked before anything is fused, a weight given for a place no list holds included.
When k or a weight is not a finite number, zero or more, or a cap (perList, perGroup,
limit) is not a whole number, zero or more, or positive infinity.
Fuses the lists. A list's items are in its own rank order, best first; an item twice in one list counts once, at its better rank. Every option is checked before anything is fused, a weight given for a place no list holds included.