Semantics Supervision 1:

From the lecture notes:
Section 2.4 2, 8, 9, 11

Section 3.4 12( e1 op e2, and if e1 then e2 else e3 ), 13, 14, choose one of 15 or 16

Extend L1 with ++, -- operations, including extending the type system. Provide updates to your preservation and progress proofs as needed.

Choose one of 2.4 4, or 5 (Both require modifications to the implementation).
Code should be submitted to me by e-mail, I only require modified files. 
Answers should be submitted as usual.