The code covering radius of an error-correcting code
is the greatest Hamming distance of a word to
its nearest codeword:
Here
is the alphabet and
is the Hamming distance.
Thus Hamming distance balls of radius
about the codewords cover
.
For the first-order Reed-Muller code on nine variables, Wang et al. (2026) proved that . Equivalently, every Boolean
function on nine variables has Boolean
function nonlinearity at most 242, and this value is attained.