Function compare_rows_rev 

pub fn compare_rows_rev(
    sort: &Sort,
    reverse: bool,
    a: &OwnedRow,
    b: &OwnedRow,
) -> Ordering

reverse=false ⇒ compare_rows(sort, a, b); reverse=true ⇒ its negation. Defined ONCE so the cursor seek direction, the overlay-add splice position, the remove-suppress equality, the start gate, and the k-way merge all agree.