Collecting water from the river in vessels with a capacity of 7 liters and 3 liters

Collecting water from the river in vessels with a capacity of 7 liters and 3 liters, how can you leave 2 liters of water in a vessel with a smaller capacity?

Let the 7 liter vessel be the first, the 3 liter vessel the second.

Both vessels are empty.

We collect the second vessel (3 liters) with water and pour it into the first, we get:

1 vessel – 3 liters (we can still hold 7 – 3 = 4 liters);

2 vessel – 0 liters.

The second time we collect water into the second vessel (capacity 3 liters), pour it into the first, we get:

1 vessel – 3 + 3 = 6 liters (we can still hold 7 – 1 = 1 liter);

2 vessel – 0.

The third time we collect water into the second vessel, pour into the first missing 1 liter, we get:

1 vessel – 7 liters;

2 vessel – 2 liters (3 – 1 = 2).