/**
 * THERE IS SOMETHING TERRIBLY WRONG WITH ME.
 */
public class test {
	public static void main(String[] args) {
		b<String,String,String> f =
			new flip<String,String,String>(new append());
		System.out.println(f._(" world", "hello"));
	}
}

class append implements b<String,String,String> {
	public String _(String a, String b) {
		return a+b;
	}
}

class flip<X,Y,Z> implements b<X,Y,Z> {
	private b<Y,X,Z> f;
	public flip(b<Y,X,Z> f) {
		this.f = f;
	}
	public Z _(X x, Y y) {
		return f._(y, x);
	}
}

interface b<X,Y,Z> {
	Z _(X x, Y y);
}

interface a<X,Y> {
	Y _(X x);
}