Quickly review the Magen Avraham ס’ שי”ח ס”ק י until “כתב הרמב”ם who quotes the מהרש”ל who learns from our Gemara that it is permitted to roast an egg on the hot tar of a roof.
Question:
Why would it be permitted according to the Rabanan?
The Magen Avraham disagrees. Why?
https://hebrewbooks.org/pdfpager.aspx?req=14325&st=&pgnum=153
Learn the משנה ברורה ס’ שי”ח ס”ק כ how we rule lhalacha
Learn the גמרא דף לט. “אמר רב נחמן (bottom of the Amud) until דף לט: מעשה (two dots)
Question:
What is the chidush that it is prohibited to immerse a pipe of cold water inside the חמי טבריא ?
Learn תוס’ דף לט: ממעשה
Is the case of immersing a pipe of cold water inside the חמי טבריא on Friday or Shabbos?
Why is the water prohibited?
Learn דף לח: “מעשה