The North Korean contributions to the Chinese Communist victory were not forgotten after the creation of the People's Republic of China in 1949. As a token of gratitude, between 50,000 and 70,000 Korean veterans that served in the PLA were sent back along with their weapons, and they later played a significant role in the initial invasion of South Korea. China promised to support the North Koreans in the event of a war against South Korea. The Chinese support created a deep division between the Korean Communists, and Kim Il-sung's authority within the Communist party was challenged by the Chinese faction led by Pak Il-yu, who was later purged by Kim.
Who led the faction that challenged Kim-Il-sung?
Pak Il-yu

In a further refinement of the direct use of probabilistic modelling, statistical estimates can be coupled to an algorithm called arithmetic coding. Arithmetic coding is a more modern coding technique that uses the mathematical calculations of a finite-state machine to produce a string of encoded bits from a series of input data symbols. It can achieve superior compression to other techniques such as the better-known Huffman algorithm. It uses an internal memory state to avoid the need to perform a one-to-one mapping of individual input symbols to distinct representations that use an integer number of bits, and it clears out the internal memory only after encoding the entire string of data symbols. Arithmetic coding applies especially well to adaptive data compression tasks where the statistics vary and are context-dependent, as it can be easily coupled with an adaptive model of the probability distribution of the input data. An early example of the use of arithmetic coding was its use as an optional (but not widely used) feature of the JPEG image coding standard. It has since been applied in various other designs including H.264/MPEG-4 AVC and HEVC for video coding.
What uses an internal memory state?
Huffman algorithm

Contact with European diseases such as smallpox and measles killed between 50 and 67 per cent of the Aboriginal population of North America in the first hundred years after the arrival of Europeans. Some 90 per cent of the native population near Massachusetts Bay Colony died of smallpox in an epidemic in 1617–1619. In 1633, in Plymouth, the Native Americans there were exposed to smallpox because of contact with Europeans. As it had done elsewhere, the virus wiped out entire population groups of Native Americans. It reached Lake Ontario in 1636, and the lands of the Iroquois by 1679. During the 1770s, smallpox killed at least 30% of the West Coast Native Americans. The 1775–82 North American smallpox epidemic and 1837 Great Plains smallpox epidemic brought devastation and drastic population depletion among the Plains Indians. In 1832, the federal government of the United States established a smallpox vaccination program for Native Americans (The Indian Vaccination Act of 1832).
Who were the Native Americans exposed to smallpox because of?
Europeans