An list of
**
increasing
**
two-digit positive integers is formed so that

-each integer in the list uses only digits from ${1, 2, 3, 4, 5, 6}$

-each of the integers in the list has its units digit is greater than its tens digit, and

-each of the digits ${1, 2, 3, 4, 5, 6}$ appears in exactly three of the integers in the list.

How many different lists are possible?

The answer is 70.

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