Creating a "if player has seen page" script in gamebook mode

Hi dear Forum,

I have tried for hours now and also searched the forum up and down but could not find the answer.

How is it possible for me to show a message only if a player has already visited another page?

So far I've been trying the following:

http://i.imgur.com/SPy1Ch4.jpg

While I think this is correct, how do I make this function "pop up" on a specific page?

Thank you all, I'm grateful for every bit of adive that enables me to continue making my little game!

You are on the right way:
gb.png

Danke dir Pertex, it works perfectly now!