How to remove the key from the `redBlackTree` with comparator" a <= b "?

[Dennis Ritchie via Digitalmars-d-learn]

On Sunday, 7 June 2015 at 18:50:47 UTC, anonymous wrote:
> On Sunday, 7 June 2015 at 18:42:58 UTC, Dennis Ritchie wrote:
>> How do I remove the key from the `redBlackTree` with 
>> comparator "a <= b" ?
>
> Do not use '<=' as a comparison function with RedBlackTree. It 
> doesn't meet the requirements.
>
> Quoting the documentation [1]:
>> Note that less should produce a strict ordering. That is, for 
>> two unequal elements a and b, less(a, b) == !less(b, a). 
>> less(a, a) should always equal false.
>
> This doesn't hold for '<='.

OK. But I want to return a `upperBound` segment with the included 
`key`. It does not suit me:

auto rbt = redBlackTree!("a < b", int)(1, 2, 3, 4, 5);
writeln(rbt.upperBound(3)); // prints [4, 5]

I want it to be so:

auto rbt = redBlackTree!("a <= b", int)(1, 2, 3, 4, 5);
writeln(rbt.upperBound(3)); // prints [3, 4, 5]

How do I do with the comparator "a < b" ?