let (++) (a,b) (c,d) = (a+c, b+d);;
let (@@) (a:float,b:float) (c:float,d:float) = (a*c - b*d, b*c + a*d);;

//2
let (--) (a,b) (c,d) = (a,b) ++ (-c,-d);;
let (/.) (a,b) (c,d) =
 if c = 0.0 && d = 0.0
 then failwith "You cannot divide by zero"
 else (a,b) @@ (c/(c*c + d*d), -d/(c*c + d*d));;

//3
let (/.) (a,b) (c,d) =
 if c = 0.0 && d = 0.0
 then failwith "You cannot divide by zero"
 else
 let denom = (c*c + d*d)
 (a,b) @@ (c/denom, -d/denom);;