4. A string contains several even natural numbers. Each number, except the leftmost one, is obtained by subtracting the largest digit of its left neighbor from it. Can the string contain more than 12 numbers?
4. Answer. Yes, it can. Solution: For example, the following sequence of 13 numbers works: 888, 880, 872, 864, 856, 848, 840, 832, 824, 816, 808, 800, 792. Note that other examples are not excluded, and it is necessary to carefully check the condition that all numbers are even.

Criteria: any correct example of a sequence - 7 points; in all other cases 0 points.