Question 102: First and fourth move in Yul Gok

I was wondering if you could help me by clarifying what exactly is the first and fourth move in Yul Gok, as written by Gen Choi Hong Hi? On every English written site on the internet, we are told to 'extend the arm'. Is this a checking block? or a measure? or something else, also after executing move 3, when you bring your legs together do you leave the arm extended or bring your hands back into a 'chunbi' type position? The translated encyclopedia of TKD written by General Choi does not specify what the move is either. Do you know where I could get an original copy of the description of pattern Yul Gok?