Create pairs out of the elements of a given list.

Input parameters:

1. Li → List whose elements to pair up.
2. Pr → Pairing mechanism to apply.
   • 0 → All
   • 1 → Diagonal
   • 2 → Upper Triangle
   • 3 → Upper Triangle Strict
   • 4 → Lower Triangle
   • 5 → Lower Triangle Strict
3. On → If true, omit any pairs containing null elements.
   •  True → Exclude
   • False → Include

Output parameters:

1. P1 → List containing the primary elements of all pairs.
2. P2 → List containing the secondary elements of all pairs.