x === y: true
x.baz: 5
z.has(five): true
z.get(five): 5
post update 1 -- y.has(three): true
post update 1 -- y.get(three): 3
post update 1 -- z.has(five): false
post update 2 -- x.has(five): true
post update 2 -- x.get(five): 5
post update 2 -- x.get(three): 4