MapSet.difference

You're seeing just the function difference, go back to MapSet module for more information.

difference(map_set1, map_set2)

difference(t(val1), t(val2)) :: t(val1) when val1: value(), val2: value()

Returns a set that is map_set1 without the members of map_set2.

iex> MapSet.difference(MapSet.new([1, 2]), MapSet.new([2, 3, 4]))
#MapSet<[1]>