**Note:** Use auxiliary predicates such as `addP`, which are defined on positive numbers. Furthermore, use the following equations and develop equations for further combinations if necessary.

~~~

1+1 =2

1+(2 * N) =2 * N+1

1+(2 * N + 1) =2 * (N+1)

1+1 =2

1+(2 * N) =2 * N+1

1+(2 * N + 1) =2 * (N+1)

~~~

2. When used in the opposite direction, e.g. with a query like `add(X, Y, pos(o(i)))`, Prolog computes all solutions, but, unfortunately, does not terminate. The reason is, that the Prolog program does not know that the sum of two positive numbers is greater than each summand, and thus increasing summands are tried.