Understanding sequential solution for the TAOCP 3 Million Men problem

Question

The problem and solution of interest is described here: What does > mean in this TAOCP solution?

Can anyone explain following points in that solution:

1. How exactly we can build (x[i], x[i+2]) for 1 <= i <= N-2 ?
2. What exactly means "merge G with it"? Provide exact algorithm for merging these two files.

3. How steps 1-4 are executed? Is it:

   if (condition 1) {
       ....
   }
   if (condition 2) {
       ....
   }
   if (condition 3) {
       ....
   }
   if (condition 4) {
       ....
   }
   

   or

   if (condition 1) {
       ....
   }
   else if (condition 2) {
       ....
   }
   else if (condition 3) {
       ....
   }
   else if (condition 4) {
       ....
   }
   

   ?

Answer 1

1. With a for loop that steps through the array and creates a new pair from the $i$th and $(i+2)$th elements, for each $i$.

2. The same as the merge step in merge sort.

3. There are no "otherwise"s in the statement in English, so there should be no else statements.