2.1 Definitions and ExamplesDefinition of a FunctionFloor and Ceiling FunctionsGreatest Common DivisorThe Mod FunctionThe Log FunctionExercises2.2 Composition of FunctionsThe Map FunctionExercises2.3 Properties and ApplicationsInjections, Surjections, and BijectionsThe Pigeonhole PrincipleSimple CiphersHash FunctionsExercises2.4 CountabilityComparing the Size of SetsSets That Are CountableDiagonalizationLimits on ComputabilityExercises