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

[anonymous via Digitalmars-d-learn]

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 '<='.