I have the following sentence:
In order to read the remainder of this book, the reader is advised to familiarize themselves with the concepts contained within this Chapter.
I want to put:
In order to read the remainder of this book, the reader is advised to familiarize themself with the concepts contained within this Chapter.
In this very great article here, it explains why you should use themself only in an informal context, and the sentence they gave supports this, however; In the sentence I have, it sounds plain wrong (as sometimes proper English tends to sound, admittedly), despite what they say. Should I still use themselves, because it is in a proper context, or am I able to use themself instead, despite its proper context?