`question about key-range lock

create table foo (c1 int)
go
insert into foo values (1)
insert into foo values (5)
insert into foo values (9)
create   clustered index foo_ci on foo(c1)
set tran isolation level serializable
begin tran
select * from foo where c1 = 5

for the above query, we know it would generate two RangeS-S,one for key 5 and the other is for key 9. that is to say it would prevent inserting values like 6,7,8 as there's a RangeS-S for key 9.

so my question is why SQL server needs the RangeS-S for key 9?  doesn't it enough just a RangeS-S for key 5 preventing the Phantom?

In other words, what will happen or the side effect if we remove the RangeS-S for key 9?

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