Definition of 99

Year 99 (XCIX) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Palma and Senecio (or, less frequently, year 852 Ab urbe condita). The denomination 99 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

In mathematics, the repeating decimal 0.999... (sometimes written with more or fewer 9s before the final ellipsis, or as 0.9, , 0.(9)) denotes a real number that can be shown to be the number one. In other words, the symbols 0.999... and 1 represent the same number. Proofs of this equality have been formulated with varying degrees of mathematical rigor, taking into account preferred development of the real numbers, background assumptions, historical context, and target audience.