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We've seen lists of symbols and lists of numbers; you can of course have a list with elements of any given type...including other structures like

<tt>

posn

</tt>

posn-s. This just uses ideas you've already learned, but in new contexts.

1. Define the type of lists of

   HTML
   <tt>

   posn

   HTML
   </tt>

   posn-s.
2. Write the templates of lists of

   HTML
   <tt>

   posn

   HTML
   </tt>

   posn-s. (NB: There are two non-primitive types here, one inductive the other a structure. So this may require two templates or one, depending on if you believe in structure templates.)
3. Write the function positive-quadrant? , which takes in a single posn and returns true only when its components are both positive.
4. Develop count-positive-quadrant , which takes a list of

   HTML
   <tt>

   posn

   HTML
   </tt>

   posn-s and returns a count of those in the upper-right quadrant.
5. Develop filter-positive-quadrant , which takes a list of

   HTML
   <tt>

   posn

   HTML
   </tt>

   posn-s and returns a list of those in the upper-right quadrant.

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