I'm currently attempting to determine whether or not my relations and tables are in BCNF, but i'm not really sure how to do it. I do have the FD's for each table. Do I have to use closure or something? I DID attempt it...is this correct? The tables are Books, Payment, Customers, Credit, Check (Credit and Check are ISAs), Write, and Order (Write and Order are relations).

Books (ID, title, author, pages, price, published)
FD: ID -> title, author, pages, price, published
title, author -> ID, pages, price, published
{ID}+?
Y = {ID}, ID -> title, author, pages, price, published =>
Y+ = {ID, title, author, pages, price, published}

Payment (ordernum, username)
FD: ordernum -> username
{ordernum}+?
Y = {ordernum}, ordernum ->username =>
Y+ = {ordername, username}

Customers (name, email, username, password, membersince, address)
FD: username -> name, email, password, membersince, address
name, address -> username, email, password, membersince, address
{username}+?
Y = {username}, username -> name, email, password, membersince, address =>
Y+ = {username, name, email, password, membersince, address}

Credit (ordernum, creditnum, expdate)
FD: ordernum -> creditnum, expdate
{ordernum}+?
Y = {ordernum}, ordernum -> creditnum, expdate =>
Y+ = {ordernum, creditnum, expdate}

Check (ordernum, checknum, accountnum)
FD: ordernum -> checknum, accountnum
{ordernum}+?
Y = {ordernum}, ordernum -> checknum, accountnum =>
Y+ = {ordernum, checknum, accountnum}

Write (ID, username, review)
FD: ID, username -> review
{ID, username}+?
Y = {ID, username}, ID, username -> review =>
Y+ = {ID, username, review}

Order (username, ID ordernum, quantity)
FD: ID, username, ordernum -> quantity
{ID, username, ordernum}+
Y = {ID, username, ordernum}, ID, username, ordernum -> quantity =>
Y+ = {ID, username, ordernum, quantity}

THANKS!