A 3-ary Boolean function ${\displaystyle f(x_{1},~x_{2},~x_{3})}$
can be expressed by means of the Walsh spectrum ${\displaystyle (r_{0},~r_{1},~r_{2},~r_{3},~r_{4},~r_{5},~r_{6},~r_{7})}$
as an arithmetical polynomial:

${\displaystyle f~(x_{1},x_{2},x_{3})~~~~=~~~~{\tfrac {1}{8}}~~{\bigg (}~~r_{0}+r_{1}(-1)^{x_{1}}+r_{2}(-1)^{x_{2}}+r_{3}(-1)^{x_{1}\oplus x_{2}}}$
${\displaystyle +r_{4}(-1)^{x_{3}}+r_{5}(-1)^{x_{1}\oplus x_{3}}+r_{6}(-1)^{x_{2}\oplus x_{3}}+r_{7}(-1)^{x_{1}\oplus x_{2}\oplus x_{3}}~~{\bigg )}}$

${\displaystyle ~\oplus ~}$ stands for the modulo-2 addition.