There should be no lose of performance, there were no reason not to use an accumulator as far as I can tell
As in Lists, it is usefull to be able to unify to map with the same elements, and fold on it.
…two set/map Usefull to explain why two sets are not equal.
Same as choose, but giving an option instead of an exception on empty map/set
I needed "choose" in my map, hence I added it, as in set.
Documenting some function, and commenting the implemantation