/(x,x) -> 1()
/(x,1()) -> x
i(/(x,y)) -> /(y,x)
i(1()) -> 1()
/(1(),x) -> i(x)
i(i(x)) -> x
/(x,/(z,y)) -> /(/(x,i(y)),z)
/(/(x,y),i(y)) -> x
/(/(x,i(y)),y) -> x