Read every skill either one names, and every skill those name, to the end of the chain; never stop at the first skill named.
Skip a skill already read in this stretch of work; never read one twice.
Run pat-down; never defer it past this reading.
Hold span-closure unrun at a start; never run it on reading it.
Enter span-closure where the end of a stretch of work is signalled ahead of it; never enter it at a start.