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 take-off 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 combination, defined as "two (or more) jumps performed in immediate succession", is executed when a skater's landing foot of the first jump is also the take-off foot of the following jump. If a skater executes one complete revolution between the jumps, the element is still a combination. The free foot can touch the ice, but there must be no weight transfer on it. The skater can also perform an Euler between jumps. If the first jump of a two-jump combination is not completed successfully, it is still counted as a jump combination. A jump sequence is executed when a skater completes two or three jumps, with no limits on the number of revolutions. The first jump, which can be any type allowed by the ISU; the second and/or third jumps must be an Axel-type jump "with a direct step from the landing curve of the first jump to the take-off curve" of the Axel. Skaters can also complete one full revolution on the ice between the jumps and their free foot can touch the ice, although without transferring their weight onto it. All jumps are considered in the order that 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, whom TV sports producer David Michaels called a true transitional figure who changed everything" because of her jumping skills, 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 stated that the ISU established the rule "in order to encourage variety and balance rather than allowing a skater to rack up credit