The Rules of Yeiush

Someone lost an item, which was worth a significant amount of money. His neighbor later revealed to him that he had seen the item on the street but didn’t bother to pick it up. This individual wants to take his neighbor to a din Torah for causing him a loss by not performing the mitzvah of hashavas aveidah . Does he have a case?

Yankel wrote an original song. For whatever reason, the song is now readily available in the public domain and can be legally downloaded for free. Yankel, however, insists that he is not amenable to this arrangement and says that he doesn’t give anyone permission to download it without payment. Is it permissible to download the song without his permission?

There is a concept found in the Gemara if “ odom memashmesh b’kiso b’chol sha’ah ”, which means that a person is always presumed to be aware of the valuable items he is carrying in his pockets and knows if he drops any money. In our times, when people are often unaware of what exactly is in their pockets, does this concept still apply?

A fellow is walking in a totally non-Jewish neighborhood and finds a pocketbook. It contains a lot of cash but no credit cards or ID. It does, however, contain a “mitzvah note” signed by “Mommy”. Is he allowed to keep it?