(VAR x y b)
(RULES
minus(x,x) -> 0
minus(s(x),s(y)) -> minus(x,y)
minus(0,x) -> 0
minus(x,0) -> x
div(s(x),s(y)) -> s(div(minus(x,y),s(y)))
div(0,s(y)) -> 0

f(x,0,b) -> x
f(x,s(y),b) -> div(f(x,minus(s(y),s(0)),b),b)

)
(COMMENT 
f(x,y,b) = x*b^(-y)
)