hw04 discuss:
  draw-astrs by template;
  then, as tail-recursive

  
  design recipe:
     http://htdp.org/2003-09-26/Book/curriculum-Z-H-13.html#node_sec_9.4

review/remember:
  lambda
  tail-recursion; using an accumulator.
  Exercise: write 'min' using an accumulator; first in Java, then in tail-recursive racket

  First-order functions: 
     Hey, check out 'sort':  
       sort strings alphabetically;
         (sort string<=? (list "hi", "bye", "Zoomba!"))
       sort by alphbetical-case-independent
         (sort (lambda (s1 s2) (string<=? (to-upcase s1) (to-upcase s2))) 
               (list "hi", "bye", "Zoomba!"))
         (list "hi", "bye", "Zoomba!"))
       alphabetical-igorning "A ", "The ":
       
     write filter-evens (think about: filter-odds, filter-primes, filter-long-strings, ...)