Explanation #1: Rashi explains - because the Torah writes "ki'Nechalim Nitayu ... ka'Ahalim Nata"

Refutation: It seems to Tosfos however, that "Ahalom" in that Pasuk is notaLashon of 'tent' (but spices).

Explanation #2: It is therefore preferable to explain that it is because the Torah juxtaposes "Mah Tovu Ohalecha" to "ki'Nechalim Nitayu".

Clarification: This is because he doesn't know from which point he erred. But if one knows that one skipped a word or a Pasuk, then one only needs to go back to the place where one erred.

Clarification (cont.): And the same applies to Hallel and Megilah.

Implied Question: This is not an episode that contradicts the ruling ...

Answer: But rather it is coming to teach us that a great man who knows that hw is able to concentrate,and who is worthy of making a name for himself, is permitted to do so.

Question: Why is not forbidden anyway because of what we learned earlier (on Daf 10:) 'One is not allowed to stand on a high place and Daven'.

Answer: That refers to standing on a chair or on a bench, but standing on a tree, which one climbed to do one's work is comparable to standing in an attic.

Clarification: La'av Davka 'One Perek' - since this goes according to Rava, and Rava himself stated earlier (on Daf 13:) that it is only the first Pasuk that requires Kavanah,and that is the Halachah.

Question: Why can we not answer that everybody else is permitted to do so,whereas workers are obligated to?

Answer: It is obvious to the Gemara that since everybody else is permitted tosay the shortened form of the Amidah, it would not be the least Chidush totellus that workers may do so even Lechatchilah.

Implied Question: Even though they are mi'd'Oraysa ...

Answer: The Chachamim have the right to negate something that is min ha'Torah, seeing as the workers are busy working for their employer.

Clarification: If you would give he reason as being becuse of 'Tirda' (worry),it would be fine...

Clarification (cont.): But now that you say the reason is because of the Mitzvah, then the same ought to apply to a widow.

Clarification: And there would be sorrow if he was not allowed to wash; and an Aveil is only forbidden to wash because of pleasure.

Clarification (cont.): Similarly, an Aveil whose hair is matted is permitted to wash it during the Shiv'ah.

Halachah: And by the same token, Rabeinu Shmuel permitted a woman who gave birth during the Shiv'ah to wash on Tish'ah be'Av.

Proof #1: And thus it is implied in Maseches Yoma (Daf 77:),which permits someone with pimples on his head to anoint himself on Yom-Kipur with impunity, despite the fact that anointing oneself on Yom Kipur is akin to drinking.

Proof #2: And so it is implied in the Yerushalmi, which restricts the prohibition of an Aveil to wash, to where he washes for pleasure, but not if it is not; and it then brings a proof from the Gemara concerning pimples that just cited.

Question: Even a proper Onan is only forbidden to eat Ma'aser (Sheini), but as far as the washing of Aveilus is concerned, it is only de'Rabbanan. In that case even if Aninus Laylah would be d'Oraysa, that would only be with regard to Ma'aser, but not with regard to washing?

Answer: If Animus Laylah would be d'Oraysa with regard to Ma'aser, the Chachamim would have had to decree with regard to other issues as well ...

Source: Because of the principle that 'Whatever the Rabbanan decreed, they decreed like the Torah law'.

Reason: In case people will come to consider him a Meyuchas (with regard to marrying a Kasherr Yisre'eilis)