prolog programming help

I have 3 tables with information as followed:

book(Code,Title,Author,Price,Format)
customer(Invoice,Initials,Surname,Street,Town)
order(Invoice,Code,Quantity).

So, for e.g, this is the query I use to to give me the title/author of a book which is available in hardback and paperback..

Code:

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book(_,Title,Author,_,pbk),book(_,Title,Author,_,hbk).

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This is the query used to return all the books in a price range 20-25..

Code:

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book(Code,_,_,Price,_),Price >= 20,Price =< 25.

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This is the query used to give details of customer who has ordered more than 1 copy of the same book

Code:

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customer(Invoice,Initials,Surname,_,_),order(Invoice,_,Quantity),Quantity >= 2.

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But im having trouble on one other query, i need to return the code,title and author of a book that has been ordered by atleast 2 customers.
Any suggesstions guys? thanks in advance.