[Pharo-users] little "challenge"

#(16 17 17 16 18 17 18 19 19 19 18 19 19 20 19 20 19 20 20 20 19 20) -> { #(17 17 16 18 17 18 19) . #(19 19 18 19 19 20 19) . #(20 19 20 20 20 19 20)} any code?