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Thanks for the help so far
So to what you explained, let's say I want to remove the grayed out text (for example if I added it in the wrong place, and I regret it ..) how can I return the text to it's regular state?

That was great answer :)
I played with all the options and it's really nice,two things though:
1) when I mark the some line in the text and choose grayed out, it draw a line on the text, which is nice, but now let's say I want to remove that line, how can I do that?
2) it also enable you to add some ...

I am using the lyx software for few weeks now, and I found it very good so far.
My only problem now is that my advisor want to edit the document with me (that is to add comments on my paper and so on...)
In Word you have the yellow mark, and the red line that can be crossed on the text.

Is ...