how do I get the difference between two R named lists?

aa<- list(a=1, b="two", c=list(3, "four"))

bb <- list(a=1, c=list(3, "four"), b="ni")

aa[!(aa %in% bb)]

REF:
https://stackoverflow.com/questions/1468856/how-do-i-get-the-difference-between-two-r-named-lists