1. Once, two elves Ilsa and Elsa, and two dwarves Bilyn and Dilyn gathered. One of them gave something to their human friend Vasily, after which each of them spoke:

- The gift was a sword.
- I didn't give anything!
- Ilsa gave a necklace.
- Bilyn gave a sword.

It is known that the elves lie when talking about dwarves, and the dwarves lie when talking about the gift. In all other cases, everyone tells the truth. Determine what was given and by whom.
Solution. The phrase "I didn't give anything" could not have been said by the elf, so it must have been said by the dwarf. Since this phrase is about a gift, it is a lie, and this dwarf must have given something to Vasily. Then the phrase "Ilse gave the necklace" is a lie, and it could not have been said by the elf. Therefore, this phrase was said by the dwarf. This means the first and last phrases were said by the elves. The first is true, as it is not about dwarves, so a sword was given. The last one is about a dwarf, so it is a lie, meaning the sword was not given by Bilyn. Therefore, the sword was given by Dilyn.

Comment. It is assumed that everyone (regardless of whether they are telling the truth or lying) speaks grammatically correct sentences, for example, an elf cannot refer to herself in the masculine form. There is no need to announce this to the children in advance, but you should answer their questions.