u/Chichmich

This one is moderately easy if you know the syntax. :)

Let’s say not all the chevrons have been written, sometimes it has been the case, sometimes not…

First, what should match:

<1 (the chevron on the right has been forgotten)
2> (the chevron on the left has been forgotten)
<3> (Even if you don’t do anything, it should be considered)

Then, what shouldn’t match:

4 (there’s no chevron at all, it’s impossible to tell if the chevrons should be there)

So this is the challenge: change the writing to put one chevron on the left et one chevron on the right:

From: <<1 2> 3 <4>

To: <1> <2> 3 <4>