A compact set 
with area
 |
created by punching a square hole of length 
in the center of a square. In each of the eight squares
remaining, punch out another hole of length 
, and so on.
Wallis Sieve
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Cite this as:
Weisstein, Eric W. "Wallis Sieve." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/WallisSieve.html