Easy Practice — Set 2

Quick Recap — Relations & Functions

• A relation from $A$ to $B$ is a subset of $A\times B$; a function assigns each input exactly one output.
• Counting: functions $A\to B$ number $|B|^{|A|}$; relations from $A$ to $B$ number $2^{|A||B|}$.
• Types: one-one (injective), onto (surjective), bijective (both).
• Composition $(g\circ f)(x)=g(f(x))$; inverse $f^{-1}$ exists iff $f$ is a bijection.