data Authors = <author>(String)+;
data Editors = <editor>(String)+;

data Title = <title>(String);

data Price     = <prices>(String);
data Publisher = <publisher>(String);



f(<bib>(x)) = <results>(g(x));
g($) = $;
g(<book>(t :: Title. a :: Authors. x :: Price. y :: Publisher) . r) = <result>(t.a) . g(r);
g(<book>(t :: Title. e :: Editors. x :: Price. y :: Publisher) . r) = <result>(t). g(r);
