[racket] about HTDP quick-sort dead loop?

Hi ,

When I read HTDP-Generative Recursion, I test quick-sort in Fig 68 and 
all is right.
But when I try to replace "<" with "<=" in function "smaller-items" and 
add new cond
"[(empty? (rest alon)) alon]" (do as the book Section 26  said), the new 
quick-sort doesn't work and
run in a dead loop.

My question is how to revise it?

Best regards

mht

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