In the solution, there is this transition:

It seems like there are some terms missing (marked in the picture). Is this a mistake?

If not, why are they not there?

In the solution, there is this transition:

It seems like there are some terms missing (marked in the picture). Is this a mistake?

If not, why are they not there?

The formulas with and without the literals you think are missing represent the same boolean function. This can be easily seen by filling in their truth tables, or by toying around with the formulas using the rules we introduces.