root:
             product   file:plan.py
             product   step:./plan.py

file:plan.py
               state = CONFIRMED
             creator   root:
                sink   step:./plan.py

step:./plan.py
               state = FAILED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   root:
              source   file:plan.py

(step:cat first > second)
               state = PENDING
                need = DEFAULT
              source   (file:first)
             product   (file:second)
                sink   (file:second)

(file:first)
               state = UNDECLARED
                sink   (step:cat first > second)

(file:second)
               state = PLANNED
             creator   (step:cat first > second)
              source   (step:cat first > second)
