racket encryption video 3/4 --- abstraction
Channel: Danny Heap
Date: 2012-03-12

video from http://www.cdf.toronto.edu/~heap/racket_lectures.html on how to define useful functions for future use encrypting graphics in DrRacket.  One function multiplies two numbers and then takes the remainder after division by a third, which turns out to be useful in re-arranging lists.  Another function uses the first to re-arrange a particular list: the 256 intensities that a colour component can take.  Quiz at:

www.cdf.toronto.edu/~heap/Racket/encryption.html    See also
www.cdf.toronto.edu/~heap/racket_lectures.html