Thanks to both of you.

@gmayor
So, yes, by "line" I mean "paragraph".
And when I say 'starts with the same text' I mean that the second paragraph (L2, which I should now call P2) must start with exactely the same chain than the one selected in L1 before executing the macro.

@Guessed
No, sorting paragraphs wouldn't be convenient, as I don't want to change the order of the other paragraphs (in my to-do list, the order is significant, so after sorting paragraphs I would lose informations).