If on day 1, God knows what my day 2 A/B choice will be (or variable X), then variable X has a value on day 1 - a value of either A or B. This value can't change.
Let's say this value is A. I CAN freely choose A or B. If I choose B, then God's foreknowledge has been compromised.
Your choice is not free, when YOU KNOW about the result, for example A, you want to choose B - and cannot. Here, really, there is no freedom of choice. But you cannot know, whether X=A or X=B. You cannot say "X=A", because you cannot know it. So, you freely choose A or B, though God knows your choice.
After all, why namely God? I sometimes can predict choice of my son well enough. He don't know yet, what will he choose, A or B, but I know, because I know him better than he himself. Today I already know, that X=A for him. Does it mean that his choice A/B is not free? No. Of course, if I shall not tell him anything.
According to Christians, the variable X (or God's knowledge of my day 2 A/B choice) gets its value BEFORE variable Y gets its value (or my day 2 A/B choice). Thus it raises the question of what happens if God knows variable X to be A and then I freely make variable Y equal to B.
You and other Christians have created a situation in which
1) variable X gets a value before variable Y
2) variable X must equal variable Y
3) variable Y can be freely chosen to be either equal or not equal to variable X
What if the book says the personage will kill another personage. Then the personage chooses to not kill the other personage?
If it were asked on day 1, "Does God know what my day 2 A/B choice will be?" Unless the answer is no, then on day 1, then what my day 2 A/B choice will be has already been established and cannot change.
Please elaborate.
Y is a function of the time. I can give more simple example: let's suppose the our person every day chooses between A and B, and Y(t) is the choice for day t. This allows you to say: Y(2) is not defined yet when t=1, Y(2) will be chosen when t=2.
X is not a function, it is a constant. By definition, we suppose that X=Y(2): it is knowledge of God (or of the father of a little child) about the decision, which the person will make at day t=2. So, you cannot say "X is already set" or "X does not have a value yet", because X does not depend on t at all: the words "already" and "yet" have no sense.
The difference between a usual father and God is only that a man cannot be absolutely sure about X value, he can make mistake - maybe, a child will choos another variant. God does not make mistakes. But if He does not say you about your future choice, I don't see any problems.
Your personage did not read this book. So, his choise is free. He can choose not to kill, but then it would be another book.
BTW, I'm not a Christian.