Relations & functions
Types of relations, one-one and onto functions, composition and inverses.
A function is one-one if different inputs give different outputs, and onto if every output in the codomain is reached.
How to do it
- Reflexive: aRa for all a. Symmetric: aRb ⇒ bRa. Transitive: aRb and bRc ⇒ aRc.
- Equivalence relation: all three.
- One-one: no two inputs share an output. Onto: every output is hit.
- f∘g means: do g first, then f.
