Hi I was programming an exercise with one of my son (well in Python.... arghhhhhh) and I end it up doing it in Pharo (I'm save now). The idea was to write one function that computes the powerset powerset(4) = a Set(a Set(1) a Set(1 2) a Set(3) a Set(2) a Set(1 3) a Set(2 3) a Set(1 2 3) a Set(4) a Set(1 4) a Set(2 4) a Set(1 2 4) a Set(3 4) a Set(1 3 4) a Set(2 3 4) a Set(1 2 3 4)) I did it without thinking too much in fact | s n ps | ps := Set new. 1 to: ((2 raisedTo: 4) -1) do: [ :i | s := Set new. n := 0. 1 to: 4 do: [ :b | n := n + 1. ((i bitAt: b) = 1 ) ifTrue: [ s add: n]. ps add: s ]]. ps but I wonder if we want to add it to our lib. Stef