public class Persian Tools ; IPersian Math , IPersian Text} ; public int Sum ( int a , int b) => a + b       ;public int Sum ( int a , int b , int c ) = a + b + c       ; ()public string ReverseText (string txt) => new string (txt.ToCharArray() . Reverse() . ToArray       ; { public string Postfix ( string txt , string Postfix) => $ " { txt } { Postfix       ; { public string Pertfix ( string txt , string Perfix) => $ " { perfix } { txt       { public class CustomTools : IPersian Math } ;  ( public int Sum ( int a , int b) => 2 * ( a+ b        ; ( public int Sum ( int a , int b , int c ) => 3* ( a + b + c        {