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

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

step:./plan.py
               state = SUCCEEDED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
           explained = yes
             creator   root:
              source   file:plan.py
             product   step:cat double.txt double.txt > quadruple.txt
             product   step:cat single.txt single.txt > double.txt
             product   step:echo something > single.txt

step:echo something > single.txt
               state = SUCCEEDED
                need = DEFAULT
           explained = yes
             creator   step:./plan.py
             product   file:single.txt
                sink   file:single.txt

file:single.txt
               state = BUILT
             creator   step:echo something > single.txt
              source   step:echo something > single.txt
                sink   step:cat single.txt single.txt > double.txt

step:cat single.txt single.txt > double.txt
               state = SUCCEEDED
                need = DEFAULT
           explained = yes
             creator   step:./plan.py
              source   file:single.txt
             product   file:double.txt
                sink   file:double.txt

file:double.txt
               state = BUILT
             creator   step:cat single.txt single.txt > double.txt
              source   step:cat single.txt single.txt > double.txt
                sink   step:cat double.txt double.txt > quadruple.txt

step:cat double.txt double.txt > quadruple.txt
               state = SUCCEEDED
                need = DEFAULT
           explained = yes
             creator   step:./plan.py
              source   file:double.txt
             product   file:quadruple.txt
                sink   file:quadruple.txt

file:quadruple.txt
               state = BUILT
             creator   step:cat double.txt double.txt > quadruple.txt
              source   step:cat double.txt double.txt > quadruple.txt
