7.13.md

(let-exp var exp body) : texp = t1
                         tvar = t1
                         tbody[tvar = t1] = t2

1. let x = 4 in (x 3)

Invalid.

2. let f = proc (z) z in proc (x) -((f x), 1)

(int -> int)

3. let p = zero?(1) in if p then 88 else 99

int

4. let p = proc (z) z in if p then 88 else 99

Invalid