MAYBE

Problem:
 f(true(),x) -> f(gt(x,0()),double(x))
 gt(s(x),0()) -> true()
 gt(0(),y) -> false()
 gt(s(x),s(y)) -> gt(x,y)
 double(x) -> doubleAkk(x,0())
 doubleAkk(0(),y) -> y
 doubleAkk(s(x),y) -> doubleAkk(x,s(s(y)))

Proof:
 Open