TeachScheme! 2002

   [We did lab BEFORE lecture on Thursday]

   Note: This lab builds on the following data definitions developed
   through section 10.2.  We wrote the definitions on the board at the
   start of lab.  The contains-doll? exercise is basically 10.2.1, but
   without referring to section 10.2.

   An inventory-rec is a (make-ir symbol number)
   (define-struct ir (name price))

   An inventory is 
     - empty, or
     - (cons inventory-rec inventory)

   Assignments: contains-doll? : inventory -> boolean
		10.2.2 [introduces pictures as values]
                10.2.3
                10.2.5 [hide until they are ready]
                10.2.7 [hide until they are ready]