Exercises (Prolog and DLP (II))

1. Variants of the 'Hello World' programs.

Design a program which has the same functionality like the program 'hello_world2',  however, without
using non-logical variable as a counter and without using the predicate 'repeat'.


2. Design a ‘hello-world’ program in which a thread prints out the text 'hello' repeatedly, 
and another thread prints out the text 'world' repeatedly.  Two threads should have
 different sleep time. The total number of output lines from these two threads is
 controlled to be about 20.  (Why not exactly 20? Find the answer if you are 
interested on it)