Alex Salkin (Strongfirst guy) just put up a great hanging leg raise progression easy to do in any doorstop. Aleks Salkin on Instagram: “Got 'Summer Six-Pack' ambitions but no pull-up bar upon which to do thy hanging leg raises? Verily I say unto thee: thou shalt try the non-…” Pavel wrote a little known book only on the hanging leg raise that I don't see mentioned often. I am still at the bent knee progression but I definitely feel the difference from just doing planks. It is a short read and a cheap kindle. https://www.amazon.com/Hard-Style-Abs-Hard-Heavy-ebook/dp/B0097AMZ7K There is also a progression where you lie on the floor while holding something. I finally found a use for the Smith machine!