## 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 sec_of_time h m s = 
	h*3600 + m*60 + s ;;

let time_of_sec s = 
	let hours = s/3600 in let minutes = (s - hours*3600)/60 in let seconds = s - hours *3600 - minutes * 60 in (hours, minutes, seconds);;

let add_times h1 m1 s1 h2 m2 s2 = 
	let sec1 = sec_of_time h1 m1 s1 and sec2 = sec_of_time h2 m2 s2 in let resultsec = sec1 + sec2 in time_of_sec resultsec ;;

```

## Exercise 3.1
```Ocaml
let add a b = 
	if a > b then 
		a-b + a/b
	else
		b-a + b/a

let test x y = (if x> y then x else y ) *(x+y);;


let f a b c =
	let g x y = (x+y)*(x-y) in 
	if a > b then 
		if b > c then (a+b)*(a-b) else (c+a) *(a-c)
	else
		if a > c then (a+b)*(a-b) else (b+c) * (b-c);;

let f a b c =
	(if a > b && if b > c then
		a + b else c + a
	 else if a > c then a + b else b + c)*
	 (if a > b && b > c then
		 a - b else a - c
	 else if a > c then a-b else b-c);;
```

### Exercise 3.2
```OCaml
(*logical and*)
# let and_if a b = 
	if a then
		b
	else false;;
val and_if: bool -> bool -> bool = <fun>

(*logical or*)
# let or_if a b =
	if a then true
	else b;;
	
val or_if: bool -> bool -> bool = <fun>


(*logical implication*)
# let imply_if a b =
	if a then b
	else true;;
val imply_if: bool -> bool -> bool = <fun>

(*logical exclusive or*)
let xor a b = 
	if a then
		if b then false else true
	else
		if b then true else false

(*logical equivalence = a b*)
let equiv a b =
	if a then b
	else
		if b then false else true (*not b*)

```

### Exercise 3.3
```Ocaml
# let max2 number1 number2 = if number1 > number2 then number1 else number2
val max2 : 'a -> 'a -> 'a = <fun>

# let min2 number1 number2 = if number1 > number2 then number2 else number1
val min2 : 'a -> 'a -> 'a = <fun>

# let max3 x y z =
	let high = if x > y then x else y in
		if high > z then
			high
		else z;;
val max3 : 'a -> 'a -> 'a -> 'a = <fun>

# let min3 x y z =
	let low = if x < y then x else y in
		if low < z then
			low
		else z;;
val min3 : 'a -> 'a -> 'a -> 'a = <fun>

# let middle3 x y z = 
	x + y + z - min3 x y z - max x y z ;;
val middle3 = int -> int -> int = <fun>

#let max4 number1 number2 number3 number4 = 
	let nb1 = max2(number1 number2) and nb2 = max2(number3 number4) in max2(nb1 nb2)

# let max4 x y z t= max2(max2 x y)(max2 z t)
val max4 : 'a -> 'a -> 'a -> 'a -> 'a = <fun>
# let min4 x y z t= min2(min2 x y)(min2 z t)

```
### Exercise 3.4
```Ocaml
let highest_square_sum x y z = 
	let sq x = x*x in 
	sq(max3 x y z) + sq(middle3 x y z)
val highest_square_sum : int -> int -> int -> int = <fun>

```