Makos 4a.
1. We spoke about the big chiddush of the A”R in Hilchos Shabbos. In short, the A”R states that there are two ‘melochos’ pertaining to cutting/tearing/ripping on Shabbos:
A- Chotech-, which only applies when cutting an object something to measure and/or in an exact line. Such as a perforated sheet or tissue.
B- Ko’rea- which only applies in a case where cutting, ungluing or taking apart any composite material. Meaning that is put together from a bunch of parts. Such as a piece of cloth that is woven from many strands.
Therefore, cutting a paper, which is not a composite, there is no issue to do so on Shabbos unless one forms something new by cutting it.
The Mishna Brurah mentions this chiddush of the A”R but does not mention the A”R’s name! See the attached PDF.
We mentioned that an Israeli Yemenite Rov, a true talmid chochom, Reb Pinchos Zevichi, writes that due to the change in the method of producing paper nowadays (it is a composite of many materials) A”R would agree that even today you would not be allowed to tear a paper on Shabbos.
It is in his book עטרת פז. ח”א.
Others who mention it:
http://www.hebrewbooks.org/pagefeed/hebrewbooks_org_51762_62.pdf
http://atranet.co.il/aviadstollman/responsan_new.asp?m=6
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2- We spoke about ‘tevilas nida’ in a ‘Mayon’ – meaning a well or spring and NOT a conventional Mikvah. Machlokes.
Interesting that in Likutei Torah the A”R says that one needs Mayim Chaim!
http://beta.hebrewbooks.org/pdfpager.aspx?req=16093&st=&pgnum=222
Rebbe’s note on this:
http://beta.hebrewbooks.org/pdfpager.aspx?req=16093&st=&pgnum=670
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3- Discussed the common universal practice of warming a Mikva- something we (correctly) take for granted that it is OK!
See here that the Shulchan Oruch/Mechaber has a big problem with it.
http://beta.hebrewbooks.org/tursa.aspx?a=yd_x5583
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4- Issue with pouring water into an ocean or river and the water not mixing.
Chasam Sofer notes that this Gemore is beyond him. See here.
http://beta.hebrewbooks.org/pdfpager.aspx?req=1839&st=&pgnum=176
We will continue this topic IY”H next week.