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Re: Chapter 1 and 2 Last Chance Review

    		    (2) Calls from outside the package may store incorrect
    			types (so even if your portable code is self-consistent
    			you could wind up with undetected type errors).
    I don't know what you mean by (2).
Let's say you're implementing a window system which has slots
WINDOW-WIDTH and WINDOW-HEIGHT.  You define these slots to be of type
integer *and* ensure that your code never puts a non-integer in them.
You still have to explicitly check the type of the slot value every
time any code that you didn't write could have run because a user
program could have put a non-integer in the slot without getting an
error in some implementations.