An arabian can be defined as a somersault that begins backwards completes a half twist before the gymnast feet reach the vertical and then continues rotating forward. /On a layout half the 180 degree twist can still be incomplete through the vertical. The main difference then between a true arabian and a back somersault with a half twist is determined by the moment the half twist is accomplished. A somersault may begin twisting on the vertical or even later. To be called an arabian the gymnast must complete the half twist before passing through the vertical.