*operation* Resource_List* required_res()
  // print resources required by all started projects
  *init* (@ new Resource_List() @)
  *traverse*
    *from* WorkFlowManagement 
      *via* Task 
      *through* -> *,startDate,* 
    *to* DateSelected
    *carry* *in* Resource_List* r
      *along* *from* Task *to* DateSelected
      *at* Task r = (@ resources; @)
  *wrapper* DateSelected
    *prefix*
      (@ return_val -> concatenate(r); @)