# In this example, the order of tuples in relation Orte is reversed by a DAC algorithm. Initially, one task is created for each tuple in this relation. Then, in each step the number of tasks is halved, merging the tuple sets of two adjacent tasks, until just one task is left.




let Tasks = Orte feed addcounter[C, 1] nest[C; Tuples]  
  addcounter[D, 2] project[C, D, Tuples] consume


while (Tasks count) > 1 do
  if ((Tasks count) mod 2) = 0 then 
    update Tasks := 
      Tasks feed filter[(.C mod 2) = 1] remove[C]
      Tasks feed remove[D] renameattr[Tuples2: Tuples] 
        mergejoin[D, C] 
        projectextend[; Tuples: .Tuples2 afeed .Tuples afeed concat aconsume]
        addcounter[C, 1] addcounter[D, 2]
        project[C, D, Tuples]
        consume
  else
    update Tasks := 
      Tasks feed head[1] 
      Tasks feed filter[(.D mod 2) = 1] remove[C]
      Tasks feed remove[D] renameattr[Tuples2: Tuples] 
        mergejoin[D, C] 
        projectextend[; Tuples: .Tuples2 afeed .Tuples afeed concat aconsume]
        addcounter[C, 2] addcounter[D, 3]
        project[C, D, Tuples]
        concat
        consume
endif
endwhile


query Tasks feed unnest[Tuples] count