Albert Y.C.Lai
The doc of deleteBy states: "The deleteBy function behaves like delete, but takes a user-supplied equality predicate." A precondition is that the user-supplied predicate is an equality predicate. (>=) is not an equality predicate, be it in the layperson sense of "it isn't analogous to (==)" or the mathematical sense of "it isn't an equivalence relation".
One could argue that this is a bad specification. The type is deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a] but there are further limitations on the arguments, and worse, the function doesn't check this and produce an error if the arguments don't conform, but just silently produces a meaningless result. -k -- If I haven't seen further, it is by standing in the footprints of giants