03
Part I: GEBChapter 3
Figure and Ground
Recursion and negative space. Primes vs Composites.
Just as Escher's art uses negative space (the background) to define the positive space (the subject), mathematics has its own 'Figure and Ground'. This chapter explores how the set of Prime Numbers (the figure) is defined by the set of Composite Numbers (the ground). It introduces the concept of Recursion: defining a set in terms of itself, like a painting that contains a copy of itself.
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"The Primes are the foreground figures..."