May one read the Megilah out of order? If one takes a break in the middle of the reading, must he start over from the beginning? May one recite the Megilah by heart, without using a text? Has a person fulfilled his obligation if he uses a Megilah that is written in Greek?

The Rabbis determined that one may not read the Megilah on Shabbat, lest he carry it to someone's house in order to hear it and thereby violate Shabbat. Accordingly, if Purim falls on Shabbat, when is the Megilah read?

A city with a wall from Joshua's time reads Megilah on the 15th of Adar; a city with a wall built after Joshua's time reads it on the 14th. What happens in a city where it's unclear when the wall was built?

If someone lives in a regular city but finds himself in a walled city for Purim, does he read on the 14th or 15th? What if he is unintentionally held back in one or the other, though he planned to leave before Purim? Are suburbs of a walled city considered part of that walled city?

When is a town allowed to read the Megilah several days before Purim? What other rules apply if they use this leniency?

The Rambam already explained that walled cities - which read the Megilah a day later than other places - are defined as such if they had a wall in the days of Joshua. Why is this so? Does it apply to Shushan, too, which did not have a wall in Joshua's time?

What berachot are said before and after reading the Megilah? What are the dates - plural - of reading the Megilah?

Who must hear the reading of the Megilah on Purim? What mitzvot does it supersede?

Last time, the Rambam explained the rule for when the infinitive is used in a beracha over a mitzvah, and when the gerund form is used. In today's shiur, the last in Hilchot Berachot, the Rambam explains several exceptions to that rule, and also tells us if one makes a beracha before doing a minhag - an ancient custom.

Sometimes the beracha before a mitzvah uses the word "al" - upon - and sometime it uses the infinitive - to do. According to the Rambam, what is the rule that determines which is used in which situation?