[Pharo-project] flatten method is kind of broken

Hi, I need to flatten a collection which does not contain other collections necessarily. The method flatten doesn't really work: #(#(1 2) #(3 4)) flatten -> #(1 2 3 4) OK #(#(1) #(2 3) #(#(4) 5) ) flatten -> #(1 2 3 #(4) 5) I would have expected something like #(1 2 3 4 5) #(1 2 3) flatten -> error #(#(1) 2 3) flatten -> error Is this the meant behavior for flatten? Any other method I could use instead? Thanks, Fabrizio