The set \( U \) of all positive integers less than or equal to 30 can be represented as:
\[ U = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30} \]
This set includes all the positive integers starting from 1 up to and including 30.