Question: Where is it derived from that one may not "mingle one joy with another" (above, 8b, 10:b)?

Answer: From Shlomo, who made his dedication party for the Beis Hamikdash the week before Sukkos rather than waiting until Sukkos and having a double celebration.

Question: Maybe it just so happened that the work was finished the week before Sukkos?

Answer: This is indeed a possibility, and the real source is based on the fact that the Pasuk uses extra words to describe the timing of the celebration.

The dedication festivities that took place the week before Sukkos included feasting on Yom Kippur. The people reasoned that it was alright because of a Kal Vachomer, but afterwards they were worried that perhaps the Kal Vachomer wasn't valid. But a Bas Kol told them that their actions were acceptable to Hash-m.

During the dedication ceremony Hash-m made it clear to all that He forgave David for his sin.

The people took leave of Shlomo twice: on 22 Tishrei and again on 23 Tishrei. This shows that if a person says good-bye to his rebbe and then ends up staying overnight he must say good-bye again the following day. This is what R. Yonasan ben Amsai and R. Yehudah ben Gerim did with R. Shimon bar Yochai.

R. Shimon was impressed with them and sent his son to them for a brachah. He found them analyzing two Pesukim and making the following conclusion: If a Mitzvah cannot be done by someone else, do it yourself, even if it means sacrificing performing a greater Mitzvah. If someone else can do it, however, it's better to give precedence to the greater Mitzvah.

Similarly, if there is a Mitzvah to be done, and it can be done by someone else, don't interrupt your learning for it. If it cannot be done by someone else, do interrupt your learning for it.

They gave R. Shimon's son what sounded like a curse, but his father explained that it was really a brachah.

R. Shimon ben Chalfta gave a brachah to Rav's son: You should never be ashamed.

A Beraisa explains what exactly is meant by "beauty care" that is permitted on Chol ha'Mo'ed: Applying eye shadow, arranging her hair, applying rouge. Some add: Shaving bodily hair.

R. Huna bar Chinena held that this permission is granted only for young women. R. Chisda disagreed and said it applies to all women, even the very old.

A Beraisa tells us that R. Yehudah permitted the lime treatment if it will be removed and give her enjoyment on Chol ha'Mo'ed. Even though it causes discomfort in the short run, it brings joy in the long run.

Question: In a Mishnah elsewhere R. Yehudah permits collecting a debt from an idolater on his holiday because it causes him to be uncomfortable. (Rule: It is forbidden to make an idolater happy on his holiday, for this encourages him to give thanks to his deity.) The Chachamim permit it, because "Even though it causes discomfort in the short run, it (elimination of debt) brings joy in the long run." In this case, the Chachamim use R. Yehudah's exact principle of short run vs. long run, and yet R. Yehudah disagrees with them!

Answer (R. Nachman bar Yitzchak): Chol ha'Mo'ed is different. Everything one does in preparation for the holiday during Chol ha'Mo'ed is essentially a trouble in the short run for pleasure in the long run.

Answer (Ravina): R. Yehudah always applies the principle of long run vs. short run. However, he disagrees with the premise that the idolater will have joy from his payment of the debt in the long run. "An idolater is forever distressed over his need to pay a debt."