Text overlaying text
I was conditionalizing every second line of an example, line by line. Someone said "why don't you use the upper shift key or the Ctrl key to select all the lines that you want". To be honest, I don't know what went wrong, but the result is that I have half a page that looks like this:

There was no Undo, and Ctrz-Z didn't work. The backup file is like this too.
I can see a double dotted line round what I think is the page frame, so it looks like frames have been duplicated and then moved on top of one another. I can't find a way to sort this out, can anyone help, please?
Thank you very much.
