Since there is only one parameter, I don’t want to name the parameter explicitly. I want to use the parameter as a place holder in the inner expression, just like <https://docs.racket-lang.org/threading/index.html?q=threading#%28part..Changing_the_threading_position%29|Threading Macros> did. I found the simplest way is to use _ as parameter name. It’s okay to use a, it or item as parameter name in this case, but I found _ visually easier to locate within the context. Maybe that’s why <https://docs.racket-lang.org/threading/index.html?q=threading#%28part..Changing_the_threading_position%29|Threading Macros> choose _ as well.