Nested Conditional Expressions

• a then-expr or else-expr can be a conditional:

      (define tax			       
        (lambda (income)		       
          (if (< income 10000) 	       
              0 			       
              (if (< income 20000)       
                  (* 20/100 income)      
                  (* 30/100 income)))))  

• What's the tax on $32,000?