(VAR x y z)
(RULES
sum(0) -> 0
sum(s(x)) -> +(sqr(s(x)),sum(x))
sqr(x) -> *(x,x)
sum(s(x)) -> +(*(s(x),s(x)),sum(x))
)
(COMMENT Example 2.20 (Sum of Square Numbers) in \cite{SK90})