The DOJ past case summary and FTC statements were examples. You are welcome to do a search for what is a monopoly or monopoly power and you will find various references to 50% but, again, none of these are going to be definitive. You can also ask
@BaldiMac where he concluded "50% share is generally considered a minimum, not definitive" as I have been in agreement with that. There are also varying regulations outside the U.S.
I never said partially. I was pointing out that the section I quoted was summarizing past case findings. Past case history can still be relevant to future cases. Yes, courts may decide to become more aggressive in the future regarding monopoly power but that remains to be seen. Various factors play into these things.
His comments didn't make my statement inaccurate e.g., the Supreme Court has a different threshold (typically only accepts around 1% to 2% of cases) for hearing cases which is irrelevant to what lower courts may take or how they may choose to rule, "Generally no less" is not definitive, etc.