Plan.md

1. Definitions
   1. Types
      1. values
      2. functions
   2. Tests
      1. Unit Tests
      2. Property Tests
2. Types and Tests
   1. Functions have types
   2. Tests in set
   3. Ways to improve a function spec:
      1. more tests
      2. smaller set
3. |A => B| ?
   1. Functions are mapping
4. Application
   1. dialCode
   2. isAdult
   3. compare
5. Further content
   1. algebraic data type: Product / Sum types
   2. Parametricity: how many implementation of map for Option?