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The circle of Willis (also called Willis' circle, loop of Willis, cerebral arterial circle, and Willis polygon) is a circulatory anastomosis that supplies blood to the brain and surrounding structures in reptiles, birds and mammals, including humans. [1] It is named after Thomas Willis (1621–1675), an English physician.

The gamma distribution is a two-parameter exponential family with natural parameters k − 1 and −1/ θ (equivalently, α − 1 and − β ), and natural statistics X and ln ( X ). If the shape parameter k is held fixed, the resulting one-parameter family of distributions is a natural exponential family .

As a way to honor key contributors including players, coaches, fans, broadcasters and announcers, National Basketball Association (NBA) teams often retire their jersey numbers, win totals or microphones. In the case of jersey numbers, they are usually no longer available for future players to wear, although they can ask for permission from ...