7.3. In a hat, there are three cards: blue, green, and red. Pete, Vasya, and Tolya were each given one of them and asked to name the colors. Pete said "blue," Vasya - "blue," and Tolya - "green." After this, the cards were put back into the hat and dealt again. This time, Pete said "blue," Vasya - "green," and Tolya - "green." It turned out that each boy received cards of different colors, and each time exactly one child was lying. Determine which card Pete did not see, which card Vasya did not see, and which card Tolya did not see.
Answer: Petya - green, Vasya - red, Tolya - blue.

Solution. Both Petya and Tolya named the same color both times, but they got different cards. This means that they each lied once. Therefore, Vasya told the truth: he had a blue card first,

| Petya | Vasya | Tolya |
| :---: | :---: | :---: |
| blue | blue | green |
| blue | green | green |

a blue card, then a green one. This means that Petya lied the first time, and he got a red card; Tolya lied the second time, and he got a red card.

Petya had red and blue cards, but not green. Vasya had blue and green cards, but not red. Tolya had green and red cards, but not blue.

Comment. Other variations of the problem differ only in the names of the colors and the characters.