(* 2.2 *)
let power30 x = 
   let square x = x*x in
   let power5 x = 
      square(square x) * x in
         power5 (power5 x) * power5 x;;

(*2.3*)
let mirror x = 
   let u = x mod 10 and d= x/10 in
      u*10+d;;

let abba x = x*100+mirror;;

let stammer x = abba(mirror x)*10000 + abba x;;

(*2.6*)
let sec_of_time h m s = h*3600+m*60+s;;
let time_to_sec s = (s/3600, s mod 3600/60, s mod 3600 mod 60);;
let add_time ha ma sa hb mb sb = time_of_sec(sec_of_time ha ma sa + sec_of_time hb mb sb);;