For instance, the span A 2,3,4,5 can be reached using λ +v (A 2,3,4,4 ), λ +u (A 2,3,3,5 ), λ +q (A 2,2,4,5 ), or λ +p (A 1,3,4,5 ).
it is desirable to apply λ +u whenever possible, because it only requires one operation.