[ Sequence ] copy

☞ a ≔ Sequence ← 1 ; 2 ; 3.
☞ b ≔ a copy.
b put: 999 at: 1.
✎ write: a, stop.
✎ write: b, stop.
Sequence ← 1 ; 2 ; 3
Sequence ← 999 ; 2 ; 3