An interesting note about the origins of the use of the Greek letter lambda in the Lambda Calculus. Alfred North Whitehead and Bertrand Russell in their magnum opus Principia Mathematica originally used the notation t(^x) (the hat ^ should be over the x, but I have no idea how to do this in HTML) for a function of x yielding t(x). Alonzo Church later modified this to ^x.t(x), but because the typesetter for his papers couldn't place the hat on top of his x, it looked like Λx.t(x). Eventually, yet another typesetter mutated this to λx.t(x), which was the notation that eventually stuck and gave its name to the entire formalism.