Question 61
Determine the maximal size of a set of positive integers with the following properties:
(1) The integers consist of digits from the set $\{1,2,3,4,5,6\}$.
(2) No digit occurs more than once in the same integer.
(3) The digits in each integer are in increasing order.
(4) Any two integers have at least one digit in common (possibly at different positions).
(5) There is no digit which appears in all the integers.
(1) The integers consist of digits from the set $\{1,2,3,4,5,6\}$.
(2) No digit occurs more than once in the same integer.
(3) The digits in each integer are in increasing order.
(4) Any two integers have at least one digit in common (possibly at different positions).
(5) There is no digit which appears in all the integers.