according to the ISU, jumps must have the following characteristics to earn the most points: they must have "very good height and very good length"; they must be executed effortlessly, including the rhythm demonstrated during jump combinations; and they must have good takeoffs and landings. The following are not required, but also taken into consideration: there must be steps executed before the beginning of the jump, or it must have either a creative or unexpected entry; the jump must match the music; and the skater must have, from the jump's takeoff to its landing, a "very good body position". Somersault-type jumps, like the back flip, are not allowed. The back flip has been banned by the ISU since 1976 because it was deemed too dangerous and lacked "aesthetic value". A jump sequence consists of "two or three jumps of any number of revolutions" and is executed when a skater's landing foot of the first jump is also the takeoff foot of the following jump. The free foot can touch the ice, but there must be no weight transfer on it and if the skater makes one full revolution between the jumps, the element continues to be deemed a jump sequence and receives their full value. The second and/or third jump must be an Axel-type jump, "with a direct step from the landing curve of the first/second jump in to the takeoff curve of the Axel jump". The skater can also perform an Euler between jumps. Both a jump combination and jump sequence can "consist of the same or another single, double, triple or quadruple jump". In their free skating programs, skaters can include up to three jump combinations in their free skating programs; one jump combination or jump sequence can include up to three jumps, while the other two can include up to two jumps each. All jumps are considered in the order they are completed. If an extra jump or jumps are completed, only the first jump will be counted; jumps done later in the program will have no value. The limitation on the number of jumps skaters can perform in their programs, called the "Zayak Rule" after American skater Elaine Zayak, has been in effect since 1983, after Zayak performed six triple jumps, four toe loop jumps, and two Salchows in her free skating program at the 1982 World Championships. Writer Ellyn Kestnbaum says the ISU established the