1. To teach
   1. Read
   2. Study
2. To present
   1. ideas
   2. solutions
   3. methods
   4. formulas
   5. answers
3. To train
   1. Apply
   2. Try it
4. To entertain
   1. to sell more books
   2. be popular
5. To CHANGE
   1. Action
   2. Effort
   3. Repetition