Oliver Janseps is a fencer and martial artist and apparently an author of these topics. HEMA or Historical Fencing is his passion sice around 2004. In this context he wrotes transcriptions and translations and also designed training manuals. Some of them are published for a wider audience. These you can find here or (the german ones) on: https://www.epubli.de/shop/autor/Oliver-Janseps/30604). He runs a big You-Tube channel which covers topics of the books in motion which he published or visa versa.