def find_sum_subseq(nums, target):
    """
    Let `nums` be a list of positive integers and let `target` be a positive integer
    Find a contiguous subsequence (of length at least 2) in `nums` whose sum is `target`
    and return the subsequence indices for slicing if exists, else return False

    We slide a variable sized window across the `nums` array and track the cumulative sum of array vals
    ensuring the window always has length at least 2. As `nums` contains only positive integers, 
    adding an element to the end of the window always increases the array sum, whilst removing an
    element from the start of the window always decreases the array sum.
    """
    low, high = 0, 2
    cum_sum = nums[0] + nums[1]
    while high < len(nums):
        # Check if the current subsequence (of length at least 2) sums to `target`
        if cum_sum == target:
            return low, high
        # If the cumulative sum is too low or our subsequence has length 2, add another element
        elif cum_sum < target or high - low == 2:
            cum_sum += nums[high]
            high += 1
        # Otherwise the cumulative sum exceeds the target and we can remove an element
        else:
            cum_sum -= nums[low]
            low += 1
    # Check if we found a suitable subsequence on the last iteration
    return (low, high) if cum_sum == target else False