Philip invented the 'lap-back' structure that allows the front and rear boards to project backwards to half the width of the spine producing a single, continuous plane when the book is fully open. This allows an image or configuration to be created across both boards, virtually uninterrupted by the spine.

The edges of the laps may be cut into a variety of shapes, interlocking if necessary, with the potential to make a book without any straight edges. As the laps act to protect the spine, it need not be lined. However, an open-backed book may have the spine painted to continue the configurations from board to board.

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First Lap-Back Model
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Le Labourd
by H. Lamant-Duhart
examples of lap-back structure
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Lap-Back Structure