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John Wallis (1616-1703), English mathematician. Wallis studied medicine and philosophy at Cambridge. After working for the Parliamentarians during the Civil War as a decoder of intercepted letters, Cromwell made him professor of geometry at the University of Oxford in 1649. In 1655 Wallis published Arithmetica Infinitorum (Arithmetic of the Infinite), which treated series, or the sum of infinite numbers, conics and the theory of numbers. In this book Wallis proposed the symbol now used to indicate an infinite number. Wallis was a founder member of the group of scientists that went on to become the Royal Society.
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