## Exercise 2.2 (Power)

```Ocaml
(*First version ; 6 multiplications*)
# let power28(x) =
	let x2 = x + x in
	let x4 = x2*x2 in
	let x8 = x4*x4 in
	let x16 = x8*x8 in
	x16*x8*x4 ;;

(*Second version ; 27 multiplications*)
# let power28(x) = x*x*x*x*x*x...*x ;;

(*Third version ; 11 multiplications*)
# let power28(x) = 
	let sq(x) = x*x in
	let pow4(x) = sq(sq(x)) in
	pow4(pow4(x))*sq(pow4(x))*pow4(x);;

(*Fourth version ; 7 multiplications*)
# let power28(x)=
	let sq(x) = x+x in
	let p4=sq(sq(x)) in
	sq(sq(p4))*sq(p4)*p4;;
```

## Exercise 2.3

```Ocaml
# (*my verison*)
# let mirror(n) = let diz = n/10 and uni = n mod 10 in uni*10 + diz;;
val mirror : int -> int = <fun>

# (*teatcher version*)
# let mirror n = 10 *(n mod 10)+n/10;;
val mirror : int -> int = <fun>
```

```Ocaml
# let abba(n) = n*100 + mirror(n) ;;
val abba: int -> int = <fun>
```

```Ocaml
# let stammer(n) = abba(mirror(n)) * 10 000 + abba(n) ;;
val stammer: int -> int = <fun>
```



## Exercice 2.6
```Ocaml
let sef_of_time h m s = 
	h*3600 + m*60 + s ;;

let time_of_sec s = 
	let hours = s/3600 and  minutes = s mod 60 and  seconds = s mod 3600 in (hours, minutes, seconds)

```