Hon tul. The names and symbolism of the Chang Hon tul refer to elements of Korean history, culture and religious philosophy. The GTF-variant of ITF practices an additional six tul. Within the ITF Taekwondo tradition there are two sub-styles: The style of Taekwondo practised by the ITF before its 1973 split with the KTA is sometimes called by ITF practitioners "traditional Taekwondo", though a more accurate term would be traditional ITF Taekwondo. After the 1973 split, Choi Hong-hi continued to develop and refine the style, ultimately publishing his work in his 1983 Encyclopedia of Taekwondo. Among the refinements incorporated into this new sub-style is the "sine wave"; one of Choi Hong-hi's later principles of Taekwondo is that the body's centre of gravity should be raised-and-lowered throughout a movement. Some ITF schools adopt the sine wave style, while others do not. Essentially all ITF schools do, however, use the patterns (tul) defined in the Encyclopedia, with some exceptions related to the forms Juche and Ko-Dang. 1969: ATA/Songahm-style Taekwondo In 1969, Haeng Ung Lee, a former Taekwondo instructor in the South Korean military, relocated to Omaha, Nebraska and established a chain of martial arts schools in the United States under the banner of the American Taekwondo Association (ATA). Like Jhoon Rhee Taekwondo, ATA Taekwondo has its roots in traditional Taekwondo. The style of Taekwondo practised by the ATA is called Songahm Taekwondo. The ATA went on to become one of the largest chains of Taekwondo schools in the United States. The ATA established international spin-offs called the Songahm Taekwondo Federation (STF) and the World Traditional Taekwondo Union (WTTU) to promote the practice of Songahm Taekwondo internationally. In 2015, all the spin-offs were reunited under the umbrella of ATA International. 1970s: Jhoon Rhee-style Taekwondo In 1962 Jhoon Rhee, upon graduating from college in Texas, relocated to and established a chain of martial arts schools in the Washington, D.C. area that practiced traditional Taekwondo. In the 1970s, at the urging of Choi Hong-hi, Rhee adopted ITF-style Taekwondo within his chain of schools, but like the GTF later departed from the ITF due to the political controversies surrounding Choi and the ITF. Rhee went on to develop his own style of Taekwondo called Jhoon Rhee-style Taekwondo, incorporating elements of both traditional and ITF-style Taekwondo as well as original elements. Jhoon Rhee-style Taekwondo is still practiced primarily in the United States and eastern Europe. 1972: Kukki-style