Hi Folks, Scientists look for recurring patterns in nature. Once a pattern is discovered, its essential ingredients are identified and formalized into a law or mathematical equation. Discovery of a pattern is important and those individuals who make such discoveries are rightfully acknowledged in our annals of science. Scientists are not the only ones that look for recurring patterns, so do functional programmers. Once a pattern is discovered, its essential ingredients are identified and formalized into a function. Long ago someone in the functional programming community discovered a pattern that has become known as the fold operation. It was an important discovery, on-par with some scientific discoveries. Who discovered the fold operation? When? /Roger