(Seven has been experimentally determined, but I can't recall where.)
I'm not sure I understand where you are going with this? Are you suggesting that a new product cannot enter a market without a number of simultaneous competitors?
If I want to roll out fibre to an area that doesn't have it, can I? If I want to build a fresh-produce store in a town that doesn't have one, then I need to find someone else to compete with?
Lots and lots of businesses operate as quasi-monopolies if you look hard enough. Especially in smaller and rural environments. Lots and lots of places have one gas station, one mechanic, one vet, one doctor, one diner and so on.
Your use of the word "require" seems difficult to implement. What if no-one wants to compete with me? If Apple stops making Macs, does MS have to stop making Windows?
HN is filled with stories of exorbitant rates from AT&T and Comcast that get slashed 70%+, speeds doubled, as soon as a newcomer is ready to offer fiber.
In fact, there was even a story here of a community where they formed a company that could not have done it, or not without a huge effort, but just hinted that they were exploring offering fiber to a town - and just that hint was enough for Comcast to say "wait, wait, we did the math and you all have been overpaying for internet!"
On that basis, the 'free market' should be called the 'free, competitive market' - without competition, it has little value. Businesses should be required to compete and to opeerate in competitive markets. Anything anti-competitive should be treated harshly.