public static boolean form ( ArrayList<Integer> al ) {
	int len = al.size();
        for ( int i=0; i<len; i++ ) {
            for ( int j=i+1; j<len; j++ ) {
                for ( int k=j+1; k<len; k++ ) {
                    if ( al.get(k)-al.get(j) == al.get(j)-al.get(i) && !al.contains(1487) ) {
                        System.out.println("form="+al.get(i)+al.get(j)+al.get(k) );
			return true;
                    }
                }
            }
        }
	return false;
    }