As a Tang Soo Do practitioner, the Chil Sung forms form part of our syllabus. They were introduced in the mid 80s by Hwang Kee. However, many TSD groups chose not to teach them and claimed the technical content wasn't very practical. I definitely feel that they are valid and have some practical techniques in there. This video is an example of Chil Sung Sah Ro (number 4). I'm posting it to get people's opinions. I'll try and put up some videos over the next few days.