Write an open sentence, put absolute value bars in it somewhere. Make sure you haven't written something impossible so as to make it always false or always true.
For example, don't write:
That is because the absolute value of anything is ALWAYS positive, hence no expression contained in absolute value can take on a negative value. The example is a sentence involving absolute value but it is a closed sentence because it is always false.
Also, don't write:
any real-valued expression
That is because no matter what is in the absolute value bars in the example, the value will always be positive. This is also a sentence that involves absolute value but is a closed sentence, this time because it is always true.
Now all you have to do is write one where you cannot say the sentence is always true or always false.
John
My calculator said it, I believe it, that settles it
