// RIGHT
use> ! os2:= OrderedSet {2, 6, 4, 10, 8}
use> ? os2-> insertAt(3, 99)
-> OrderedSet{2,6,99,4,10,8} : OrderedSet(Integer)
use> ? os2-> insertAt(3, 99)->at(3)
-> 99 : Integer
// WRONG
use> ! sq2:= Sequence {2, 6, 4, 10, 8}
use> ? sq2-> insertAt(3, 99)
-> Sequence{2,6,4,99,10,8} : Sequence(Integer)
use> ? sq2-> insertAt(3, 99)->at(3)
-> 4 : Integer
Thanks for your attention!
Fernando Brito e Abreu