title: prolog sum & sub using successors?
body: <p>what is substraction and summation using successors , can any one show me an example for that i know how to do it the normal way .</p>
  
  <p>/* sub(X, Y, Z) ---subtraction                        */</p>
  
  <p>sub(X, Y, Z) :- add(Y, Z, X).</p>