“Rav Moshe has no intention of counting the city as was evident in his first teshuva. But if one would count and have 600,000 in the streets than Rav Moshe would have forbade the eruv. And it would be null according to his opinion.”
No. Rav Moshe did not need to count the numbers, because his first teshuvah was regarding Manhattan, where he realized that it was encompassed by mechitzos, and so the numbers are irrelevant. Only regarding Brooklyn did he need to calculate.
“Some people use this paragraph as way to calculate, but that is not the point. Such would only achieve that it is not a reshus harrabim beyond any doubt. It wouldn’t rule out a safek doraissa and it ignores all the nuance of the first teshuva. Additionally, there is no statistical rule here. Rav Moshe lists five different activities to count. In two different places. And three estimates. Since it has no practical application, there is no reason to be clear about it. The point is to get the idea.”
Absolute gibberish. No. Rav Moshe’s teshuvos are only about reshus harrabim, and that some may perceive that it is a reshus harabbim, and not about safek d’Oraysa. It has everything to do with statistics. If an area of 12 mil by 12 mil has a population of three million, then Rav Moshe maintained that it is a reshus harabbim. If a large city contained less than three million than he would not recommend an eruv be established (Rav Moshe never argued that it is a safek d’Oraysa, only that one may think that it is a d’Oraysa, hence it is more like a gezeira not to make one). A sratya would require 600,000 traversing therein to be classified as a reshus harabbim. You do not, “get the idea.”