Chapter 3 section 5 Exercise 5 answer help

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Exercise 5.5 : Suppose we modified Algorithm 20 (BNCF decomposition) so
that instead of decomposing a relation R whenever R was not in BCNF, we only
decomposed R if it was not in 3NF. Provide a counterexample to show that this
modified algorithm would not necessarily produce a 3NF decomposition with
dependency preservation.