type Person = String
type Book = String
type Database = [(Person, Book)]

loan :: Database -> Person -> Book -> Database
returnBook :: Database -> Book -> Database
loanedBooks :: Database -> Person -> [Book]
{-
loanee :: Database -> Book -> [Person]
isAvailable :: Database -> Book -> Bool
worstReader :: Database -> Person
-}
loan db person book = (person,book):db

returnBook db book
	|snd(head db) == book 		= tail db
	|otherwise 					= (head db) : (returnBook (tail db) book)

loanedBooks db person
	|length db == 0				= []
	|fst(head db) == person 	= snd(head db) : loanedBooks (tail db) person
	|otherwise 					= loanedBooks (tail db) person

loanee db book
	|length db == 0				= []
	|snd(head db) == book 		= fst(head db) : loanee (tail db) book
	|otherwise					= loanee (tail db) book