Pair up items in a given list based on an index offset.

Input parameters:

1. Li → List whose items to pair up.
2. F1 → Offset of primary items. Positive offsets remove the leading items, while negative offsets remove the trailing items.
3. F2 → Offset of secondary items. Positive offsets remove the leading items, while negative offsets remove the trailing items.

Output parameters:

1. L1 → List containing the primary elements of all pairs.
2. L2 → List containing the secondary elements of all pairs.