Xerography or electrophotography is a dry photocopying technique. Its fundamental principle was invented by Hungarian physicist PÃ¡l SelÃ©nyi and based on SelÃ©nyi's publications Chester Carlson applied for and was awarded U.S. Patent 2,297,691 on October 6, 1942. The technique was originally called electrophotography.
A retrospective, generally, is a look back at events that took place, or works that were produced, in the past. As a noun, retrospective has specific meanings in medicine, software development, popular culture and the arts. It is applied as an adjective, synonymous with the term retroactive, to laws, standards, and awards.
Retrograde spondylolisthesis, or retrolisthesis, is the condition or problem that results when one vertebra (spinal bone) slips backward in relation to the vertebra that is below it. This is a rather rare and unusual problem compared to the more common antegrade spondylolisthsis.ypically and traditionally the term spondylolisthesis by definition means the forward slippage of one vertebra in relation to the one below it, but the additional term antergrade is added to clarify the direction of abnormal movement because of the occasional occurrence of backward movement.