[ Sequence ] replace: [ Number ] length: [ Number ] with: [ Sequence ]

>> x := Sequence ← 1 ; 2 ; 3 ; 4 ; 5.
>> z := Sequence ← 9.
>> y := x replace: 2 length: 1 with: z.
Out write: y, stop.
Sequence ← 1 ; 9 ; 3 ; 4 ; 5