A Bochner-Riesz mean of order 
and radius 
is the Fourier multiplier
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initially defined for a Schwartz function 
, where 
is the positive part.
The Fourier transform here uses 
. The multiplier tapers to zero at the boundary of the frequency ball.
The order-zero convention instead uses its characteristic
function.
The Bochner-Riesz conjecture concerns uniform operator norms as 
varies. The corresponding maximal operator
is
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