Pdict inside Pdict

Hi,
I have the following Pdict of Pdicts:

(

a = Pdict(

       (

      

             groupA: Pdict(

                    (groupA1: Pseq([1,2,3]),

                    groupA2: Pseq([4,5,6])

                    ),

                    Pseq([\groupA1,\groupA2])

 

             ),

            

             groupB: Pdict(

                    (groupB1: Pseq([7,8,9]),

                    groupB2: Pseq([10,11,12])

                    ),

                    Pseq([\groupB1,\groupB2])

             )     

            

       ),

       Pseq([\groupA,\groupB],inf)

);

      

a.asStream.nextN(20)

 

)

I want to get 1 value from each of the Pseq, then, when all 4 have been evaluated, get the second value of each, etc. But instead I get all of the first, then all of the second, etc. Any ways around it?
thanks
Uri