Problem 4: Combining booleans

For is_over.

||, &&, and <>

Once you already have the values you need, combining them into a single bool needs no pattern matching. OCaml's boolean operators do the job directly.

let a = true and b = false in
a || b   (* true  - at least one is true *)
a && b   (* false - both must be true *)
a <> b   (* true  - true when they differ *)