(from AG01 3.48)
(VAR x y)
(RULES
f(0) -> true
f(1) -> false
f(s(x)) -> f(x)
if(true,s(x),s(y)) -> s(x)
if(false,s(x),s(y)) -> s(y)
g(x,c(y)) -> c(g(x,y))
g(x,c(y)) -> g(x,if(f(x),c(g(s(x),y)),c(y)))
)