Before revision: [ he successful use of a boat to cross a river requires, if the boat is a rowboat, that the oars and rowlocks be present and unbroken, and that they fit each other.
After revision: John McCarthy gives the following motivating example, in which it is impossible to enumerate all the circumstances that may prevent a rowboat from performing its ordinary function:"T[ he successful use of a boat to cross a river requires, if the boat is a rowboat, that the oars and rowlocks be present and unbroken, and that they fit each other.