Right-reversible functions: Surjective

What's the point of a high-school styled "onto" function when it comes to programs? Answer: those are functions we can reverse! Take all those familiar pictures from algebra and join us in looking at solving equations, reversing operations, and modeling the flow of information through the what experts call "surjective" functions and "epimorphisms". After this come back to see the related approaches with injective and bijective functions.