more information than can actually be feasibly remembered, a priority system is implemented that allows the user to ensure that the most important information is remembered when they can't review all information in the system. Algorithms The specific algorithms SuperMemo uses have been published, and re-implemented in other programs. Different algorithms have been used; SM–0 refers to the original (non-computer-based) algorithm, while SM-2 refers to the original computer-based algorithm released in the 1987 (used in SuperMemo versions 1.0 through 3.0, referred to as SM-2 because SuperMemo version 2 was the most popular of these). Subsequent versions of the software have claimed to further optimize the algorithm. Piotr Woźniak, the developer of SuperMemo algorithms, released the description for SM-5 in a paper titled Optimization of repetition spacing in the practice of learning. Little detail is specified in the algorithms released later than that. In 1995, SM-8, which capitalized on data collected by users of SuperMemo 6 and SuperMemo 7 and added a number of improvements that strengthened the theoretical validity of the function of optimum intervals and made it possible to accelerate its adaptation, was introduced in SuperMemo 8. In 2002, SM-11, the first SuperMemo algorithm that was resistant to interference from the delay or advancement of repetitions was introduced in SuperMemo 11 (aka SuperMemo 2002). In 2005, SM-11 was tweaked to introduce boundaries on A and B parameters computed from the Grade vs. Forgetting Index data. In 2011, SM-15, which notably eliminated two weaknesses of SM-11 that would show up in heavily overloaded collections with very large item delays, was introduced in Supermemo 15. In 2016, SM-17, the first version of the algorithm to incorporate the two component model of memory, was introduced in SuperMemo 17. The latest version of the SuperMemo algorithm is SM-18, released in 2019. Description of SM-2 algorithm The first computer-based SuperMemo algorithm (SM-2) tracks three properties for each card being studied: The repetition number n, which is the number of times the card has been successfully recalled (meaning it was given a grade ≥ 3) in a row since the last time it was not. The easiness factor EF, which loosely indicates how "easy" the card is (more precisely, it determines how quickly the inter-repetition interval grows). The initial value of EF is 2.5. The inter-repetition interval I, which is the length of time (in days) SuperMemo will wait after the previous review before asking