(VAR x y z)
(RULES
prime(0) -> false
prime(s(0)) -> false
prime(s(s(x))) -> prime1(s(s(x)),s(x))
prime1(x,0) -> false
prime1(x,s(0)) -> true
prime1(x,s(s(y))) -> and(not(divp(s(s(y)),x)),prime1(x,s(y)))
divp(x,y) -> =(rem(x,y),0)
)

(COMMENT Example 2.29 (Prime Numbers) in \cite{SK90})