public  <T> Fn2<T,Fn1<T,T>,T> applyTwice(){
     return  (a,b) -> b.apply(b.apply(a));
}

this.<Integer>applyTwice().apply(10,(Integer a)->a+3);
//16


//using methods results in better type inference..

public static <T> T twice(T a,Fn1<T,T> fn){
        return   fn.apply(fn.apply(a));
}

twice(10,a->a+3);
//16

twice("HEY",a->a+ " HAHA"));
//HEY HAHA HAHA