I really do not have any Gemara to look this up, and  it occurs to me  that without a Gemara to look this up I might be wrong. Still I would like to suggest this idea: Abyee in Bava Batra pg 24 derives from a mishna that רוב וקרוב הולכין אחר הרוב what does that mishna say? It says דם הנמצא בפרוזדור ספיקו טמא שהזקתו בא מן המקור the Mishna says there is a חזקה and that חזקה makes the blood to be a doubt. And Abyee derives from this a ''most'' רוב is no doubt. רוב וקרוב הולכין אחר הרוב  Thus what this must mean is from the middle of the hallway and upwards, the blood is a doubt because of the  חזקה/ And from the middle and downwards the blood is definitely impure because of there is a "most". Most of the blood in that area is from the source. This fits in the Gemara in Bava Batra and is what Rav Huna said דם הנמצא בפרוזדור מן הלול ולמעלה ספיקו טמא מן הלול ולמטה ספיקו בודאי טמא that would be because from the middle and down there is a  חזקה ורוב and from the middle and up there is only a  חזקה

This seems clear if there would only be the Gemara in Bava Batra. But Abyee asks on Rav Hunaa in Nida pg 17b."if you go by a doubt then the blood found in entire hallway should be impure. If you go by חזקה then the blood found in the lower area should be considered impure and blood found in the upper area should be considered definitely pure. This sounds more like a question on the Mishna. How is it that the Misshan says because of a חזקה there is a doubt? Rather is we have a חזקה there should be no doubt. And if we have a doubt then there is no חזקה This I think explains why the Rambam brings the law as stated by Rav Huna and ignores the question of Abyee, The reason is that Abyee himself clearly agrees with the explanation of Rav Huna in the Mishna in Bava Batra. For there it is Abyee himself who says from the Mishna we learn.רוב וקרוב הולכין אחר הרוב That must mean that even Abyee thinks חזקה would not be enough to say the blood is definitely impure and we need a "most "also. This is exactly like Rav Huna. So Abyee asked his question in Nida 17 and then later agreed with Rav Huna. 

I should mention here that I do not recall all these gemaras off hand but rather aw them in the book of Rav Shach in Laws of Forbidden Relations 5 law 5. There I see he has a deep explanation of the Rambam. But here I was concentrating just on the statements of Abyee and Rav Huna. Just the logistics, not the deeper reasons for what they are saying. That I leave to Raav Shach. 

  Some people have noticed the problems with Kant's way of showing how and why principles of science work. This started a long time ago. The issue is this do we know principles like space, time, causality by induction or a priori reasons. Induction does not work as Hume showed, so Kant tried the a priori approach. The ways he goes about this are considered to be flimsy. Some people are even harsh about this. Danny Frederick wrote that the way Kant does this is  invalid and dogmatic.  So I wonder why the Kelley Ross's  approach [based on Jacob Fries and Leonard Nelson] is not more looked into. This is thoroughly Kantian, but   corrects this one area by the idea of immediate non intuitive knowledge. I would think that people that are Kantians would look into this approach.`

i realize to some extent that the whole Friesian approach has taken a long time to get into shape. You can see this yourself if you look at Fries. And as for Leonard Nelson, well things are a lot better but still there was a lot of difficulty when Relativity came on the scene. Altogether would say that the Kelley Ross approach puts it altogether in the best way  the link is to the general information site of dr ross but you might take a look at his phd thesis at that site which has a lot more detail. 

[I was motivated to mention this because Fries and Nelson were both mentioned by an Analytic philosopher] and that fellow also noticed the Nelson Affair. [Nelson was a pariah for the philosophers at  Gottingen. but very much in favor by David Hilbert. Personally I would go with David Hilbert any day of the week.

 z81 music file  z81 nwc

dipping in vessels as far as a mikve/goes is a problem

טובל בכלים dipping in vessels as far as a mikve/goes is a problem/ The major problem comes from the fact that a lot of mikvot are made with a separation between the concrete structure of the mikve and the ground. But this problem would exist anyway [even without that plastic that they put between the walls of the mikve and the ground]. Though I admit is is hard to imagine how all women would go to the sea after their period. One might make a mikve with a thin layer of concrete such that if it would be pulled up it would fall apart. [That would make the mikve ok since that concrete structure would not be a vessel.].

I am tired when I get back from the sea so i is hard for me to learn Torah this minute. So I thought to take a few minutes to explain a very important aspect of all this. A separation between one's body and the water is only a separation is it is  רוב הגוף ומקפיד stops the water from touching most of the body and one wants the water not to touch. If the clothing stops the water from touching only less than most of the body and one wants the water not to touch that makes the dipping not valid by a decree from the sages. but what you usually have with clothing is the water touches all of the body and one does not mind. that is not even a decree. So a woman can go to the sea with her regular swim suit even during the day of the seventh day and that is a valid dipping--if she dips in all of her body including her head.

i mean to say that if the period is less than seven days [which is usual]then she goes into a natural body on water even during the seventh day and becomes pure at night. but in the unusual situation that she sees again  after that then she waits a day שומרת יום כנגד יום and  goes again into water. If again she sees then again waits a day and again into water. But if she sees for three days then that is a zava and she  needs seven clean days --that means to check on the first day and seventh. If all those days are clean then she goes into a natural body of water But here I have again a problem because at that point she needs a spring. Not a river, nor even the sea but an actual spring. מים חיים   [well as rivers are concerned, that is an argument among the rishonim since rivers are fed from springs underneath them.] 

 I have thought about spheres in higher dimensions for  along time--that is the subject called homotopy but never came to any new ideas there except that the more symmetries you have in higher dimensions the less fields should be available which would limit any worlds there. So you can see why a world like in String Theory with 10 dimensions should still be limited to 3 space and one time just to have a place to have interesting results. Knots is a good example where adding dimensions makes a place where you can not have knots . They can slip.

מוקצה מחמת גופו would be coins on Shabat. But that itself is an argument between Beit Shamai and Beit Hillel concerning  bones. To Rashi that refers to bones that are totally inedible. And yet and thus. מוקצה מחמת גופו. In the Mishna Beit Hillel forbids and then the Gemara turns to Mishna around so that Beit Hillel turn out to be the ones who permit. And that goes along with the regular law that to R. Shimon Muktze only applies to Yom Tov. 

Still there are opinions in the Gemara that limit what R Shimon says--even though everyone agrees that the law is like him. So I have never written about this because people that want to be strict have some opinions to depend on. It is just that I am not looking for ways of being extra stringent. What the Torah forbids is enough for me