Computer Science about Functional language FL expression / Type systems

You have time, I'd really appreciate it if you could give me the specific answer.

S def 2xyz. xz(yz), I def 2x. x If the expression SII in the functional language FL has a principal type, find it. If not, write the reason along with the type reconstruction process. Reference: As you can see, SII is reduced to II (II) in one step, and II (II) has the principal type a a. This question is motivated by checking whether the converse of the main part of the contraction theorem, that is, "if M is reduced to N in one step and N: T, then M: 1 is always the case". III. (var) , : : (con) c: ,: TE M2: list(t) (list) TEM:: M2 : list(T) , : ' : (abs) TE (Ax. M): (I' T) : ' : ' (app) (MN): (nil) TE nil: list(T) TEL: bool : : (if) TE (if L then M else N): 1 TEN: T' , : ' : (let) TE (let x = N in M): T TEL: list(11) TEM: T2 T, X1: T1, X2: list(11) + N: T2 TF (case L of nil = M | x1 :: X2 = N): T2 (case)