👉 In mathematics, a unpilled pile is a set of n + 1 elements where each element appears exactly once in the sequence. This means that there are no gaps or overlaps between the elements. For example: - A unpilled pile of size 3 is {a, b, c}. - A unpilled pile of size 4 is {a, b, c, d} (since a and d appear twice). - A unpilled pile of size 5 is {a,
