def collapse_ranges(numbers: list[int]) -> list[tuple[int, int]]:
    # This function turns an ordered list of numbers into a list of ranges.
    # For example, [1, 2, 3, 5, 6, 7, 9] becomes [(1, 3), (5, 7), (9, 9)]
    if not numbers:
        return []
    ranges = []
    start = end = numbers[0]
    for number in numbers[1:]:
        if number == end + 1:
            end = number
        else:
            ranges.append((start, end))
            start = end = number

    ranges.append((start, end))

    return ranges