Aigosumi joseki

Kosumi against kosumi  

We're talking about this . Jowa used it successfully and there are no weaknesses in it. It was played often around 1820, and then dropped out of fashion, possibly because it was too slow. But Chang Hao played it in 2002. One can guess that increases in komi cause trials to be made of discarded joseki, by White.

This pattern can give rise to Kaizen's Heavy Plastering.

Kosumi as follow-up  

is a common way to defend when is in place. (Another rarely seen joseki move.) It is sometimes used with a stone at a as well. Most occurrences of kosumi against kosumi may not feature this exact configuration, but are related to these examples as most often White has stones along the upper side, many modern examples feature as the border of a framework.

Modern example